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Derivatives Instruments (Notional Volumes of Outstanding HFT Derivatives) (Details) - HFT derivatives MWh in Millions, MMBTU in Millions | 12 Months Ended
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Dec. 31, 2019 MMBTU MWh
Natural gas | Purchases | 2020 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 424
Natural gas | Purchases | 2021 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 84
Natural gas | Purchases | 2022 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 56
Natural gas | Purchases | 2023 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 41
Natural gas | Purchases | 2024 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 26
Natural gas | Sales | 2020 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 345
Natural gas | Sales | 2021 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 33
Natural gas | Sales | 2022 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 9
Natural gas | Sales | 2023 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 2
Natural gas | Sales | 2024 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MMBTU | 2
Power | Purchases | 2020 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 1
Power | Purchases | 2021 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 0
Power | Purchases | 2022 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 0
Power | Purchases | 2023 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 0
Power | Purchases | 2024 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 0
Power | Sales | 2020 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 1
Power | Sales | 2021 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 0
Power | Sales | 2022 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 0
Power | Sales | 2023 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 0
Power | Sales | 2024 |
Derivative [Line Items] |
Notional volumes of outstanding derivatives that are expected to settle | MWh | 0

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