Variable Interest Entities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Variable Interest Entity [Line Items]
Income (loss) before income taxes	$ 65.3	$ 4.5
SunCoke Middletown [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage (in hundredths)	0.00%
Income (loss) before income taxes	$ 16.2	$ 18.0
Vicksmetal Armco Associates [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage (in hundredths)	50.00%