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Derivatives (Notional Volumes of Outstanding HFT Derivatives) (Details) - Designated as Hedging Instrument [Member] - Held for Trading Hedge [Member] MWh in Millions, MMBTU in Millions | 12 Months Ended
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Dec. 31, 2016 MMBTU MWh
Natural Gas [Member] | Sales [Member] | 2017 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 202
Natural Gas [Member] | Sales [Member] | 2018 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 20
Natural Gas [Member] | Sales [Member] | 2019 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 16
Natural Gas [Member] | Sales [Member] | 2020 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 12
Natural Gas [Member] | Sales [Member] | 2021 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 1
Natural Gas [Member] | Cost of Sales [Member] | 2017 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 270
Natural Gas [Member] | Cost of Sales [Member] | 2018 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 69
Natural Gas [Member] | Cost of Sales [Member] | 2019 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 54
Natural Gas [Member] | Cost of Sales [Member] | 2020 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 45
Natural Gas [Member] | Cost of Sales [Member] | 2021 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 45
Power [Member] | Sales [Member] | 2017 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 4
Power [Member] | Sales [Member] | 2018 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Power [Member] | Sales [Member] | 2019 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Power [Member] | Sales [Member] | 2020 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Power [Member] | Sales [Member] | 2021 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Power [Member] | Cost of Sales [Member] | 2017 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 3
Power [Member] | Cost of Sales [Member] | 2018 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Power [Member] | Cost of Sales [Member] | 2019 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Power [Member] | Cost of Sales [Member] | 2020 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0
Power [Member] | Cost of Sales [Member] | 2021 |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh | 0

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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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- Details
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