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Risk Management Activities (Narrative) (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020
Derivative [Line Items] |  |
Limit of GCA Volumes | 20.00% |
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net | $ 0.0 | $ 0.0
Minimum |  |
Derivative [Line Items] |  |
Commodity Contract Length | 5 years |
Maximum |  |
Derivative [Line Items] |  |
Commodity Contract Length | 10 years |
Interest Rate Swap |  |
Derivative [Line Items] |  |
Derivative, Notional Amount | $ 500.0 |

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