Acquisitions (Schedule of Non-Controlling Interest) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Subsidiary, Sale of Stock [Line Items]
Net income attributable to SunCoke Energy, Inc.	$ (2.7)	$ (163.0)	$ 8.7	$ (150.9)
Public Unit Purchase Program
Subsidiary, Sale of Stock [Line Items]
Net income attributable to SunCoke Energy, Inc.		(163.0)		(150.9)
Increase (decrease) in SunCoke Energy, Inc. equity for the change in ownership interest in the Partnership		0.0		182.5
Change from net (loss) income attributable to SunCoke Energy, Inc. and transfers from noncontrolling interest		$ (163.0)		$ 31.6