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Derivatives - Net Gain (Loss) (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2020 | Mar. 31, 2019
Derivative [Line Items] |  |
Derivative, (loss) gain on derivative, net | $ 3.8 | $ (5.7)
Commodity Contract [Member] |  |
Derivative [Line Items] |  |
Derivative, (loss) gain on derivative, net | 9.0 | (5.5)
Commodity Contract [Member] | Glencore [Member] |  |
Derivative [Line Items] |  |
Derivative, (loss) gain on derivative, net | 12.6 | (1.0)
Foreign Exchange Contract [Member] |  |
Derivative [Line Items] |  |
Derivative, (loss) gain on derivative, net | $ (5.2) | $ (0.2)

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + Details
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