Variable Interest Entities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Income before income taxes	$ 69.2	$ 237.9	$ 162.7
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	$ 52.2	$ 58.4	$ 61.7
Vicksmetal Armco Associates [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage	50.00%