Variable Interest Entities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Income before income taxes	$ 237.9	$ 162.7	$ 32.3
SunCoke Middletown [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage	0.00%
Income before income taxes	$ 58.4	$ 61.7	$ 66.0
Vicksmetal Armco Associates [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage	50.00%

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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