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Derivatives - Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Due to affiliate, current	$ 50.7	$ 21.7
Due to affiliate, noncurrent	14.3	0.1
Not designated as hedging instrument [Member]
Derivative [Line Items]
Derivative asset	29.1	15.2
Derivative liability	157.0	16.7
Not designated as hedging instrument [Member] | Commodity contract [Member]
Derivative [Line Items]
Derivative asset	28.8	12.8
Derivative liability	156.5	16.7
Not designated as hedging instrument [Member] | Foreign exchange contract [Member]
Derivative [Line Items]
Derivative asset	0.3	2.4
Derivative liability	0.5	0.0
Glencore [Member] | Commodity contract [Member]
Derivative [Line Items]
Due to affiliate, current	31.7	11.3
Due to affiliate, noncurrent	$ 14.9	0.1
Due from affiliate, current		1.2
Due from affiliate, noncurrent		$ 1.7

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