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Derivatives - Assets and Liabilities (Details) - USD ($) $ in Millions | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Derivative [Line Items] |  |
Due from affiliates | $ 15.0 | $ 30.1
Due from affiliates, noncurrent | 1.3 | 0.5
Not Designated as Hedging Instrument [Member] |  |
Derivative [Line Items] |  |
Derivative asset | 18.0 | 19.7
Derivative liability | 5.7 | 4.2
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] |  |
Derivative [Line Items] |  |
Derivative asset | 17.0 | 19.7
Derivative liability | 5.7 | 3.6
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] |  |
Derivative [Line Items] |  |
Derivative asset | 1.0 | 0.0
Derivative liability | 0.0 | 0.6
Glencore [Member] | Commodity Contract [Member] |  |
Derivative [Line Items] |  |
Due from affiliates | 0.1 | 0.2
Due from affiliates, noncurrent | $ 1.3 | $ 0.5

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