Consolidated Statements of Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Retained Earnings (Deficit)	Total  SunCoke Energy, Inc.  Equity	Non-controlling Interests
Beginning balance, shares at Dec. 31, 2018		72,233,750	7,477,657
Beginning balance at Dec. 31, 2018	$ 682.7	$ 0.7	$ (140.7)	$ 488.8	$ (13.1)	$ 127.4	$ 463.1	$ 219.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(147.6)					(150.9)	(150.9)	3.3
Currency translation adjustment	(0.8)				(0.8)		(0.8)
Cash distribution to noncontrolling interests	(14.2)							(14.2)
Share-based compensation expense	3.3			3.3			3.3
Share issuances, net of shares withheld for taxes, shares		352,971
Share issuances, net of shares withheld for taxes	(1.7)			(1.7)			(1.7)
Simplification Transaction:
Share issuances, for the acquisition of Partnership public units, shares		24,818,149
Share issuances, for the acquisition of Partnership public units	0.0	$ 0.3		182.2			182.5	(182.5)
Share issuances, for the final Partnership distribution, shares		635,502
Transaction costs	(5.4)			(5.4)			(5.4)
Deferred tax adjustment	43.7			43.7			43.7
Share repurchases, shares		0	2,066,475
Share repurchases	(13.2)		$ (13.2)				(13.2)
Ending balance, shares at Sep. 30, 2019		98,040,372	9,544,132
Ending balance at Sep. 30, 2019	546.8	$ 1.0	$ (153.9)	710.9	(13.9)	(23.5)	520.6	26.2
Beginning balance, shares at Jun. 30, 2019		98,036,174	7,477,657
Beginning balance at Jun. 30, 2019	722.8	$ 1.0	$ (140.7)	709.7	(13.0)	139.5	696.5	26.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(163.1)					(163.0)	(163.0)	(0.1)
Currency translation adjustment	(0.9)				(0.9)		(0.9)
Share-based compensation expense	1.2			1.2			1.2
Share issuances, net of shares withheld for taxes, shares		4,198
Share issuances, net of shares withheld for taxes	0.0			0.0			0.0
Simplification Transaction:
Share repurchases, shares		0	2,066,475
Share repurchases	(13.2)		$ (13.2)				(13.2)
Ending balance, shares at Sep. 30, 2019		98,040,372	9,544,132
Ending balance at Sep. 30, 2019	546.8	$ 1.0	$ (153.9)	710.9	(13.9)	(23.5)	520.6	26.2
Beginning balance, shares at Dec. 31, 2019		98,047,389	13,783,182
Beginning balance at Dec. 31, 2019	518.4	$ 1.0	$ (177.0)	712.1	(14.4)	(30.1)	491.6	26.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	12.3					8.7	8.7	3.6
Reclassifications of prior service benefit and actuarial benefit amortization to earnings, net of tax	0.1				0.1		0.1
Currency translation adjustment	(1.9)				(1.9)		(1.9)
Share-based compensation expense	2.9			2.9			2.9
Share issuances, net of shares withheld for taxes, shares		125,168
Share issuances, net of shares withheld for taxes	(0.3)			(0.3)			(0.3)
Simplification Transaction:
Share repurchases, shares		0	1,621,300
Share repurchases	(7.0)		$ (7.0)				(7.0)
Dividends	(15.2)					(15.2)	(15.2)
Ending balance, shares at Sep. 30, 2020		98,172,557	15,404,482
Ending balance at Sep. 30, 2020	509.3	$ 1.0	$ (184.0)	714.7	(16.2)	(36.6)	478.9	30.4
Beginning balance, shares at Jun. 30, 2020		98,172,557	15,404,482
Beginning balance at Jun. 30, 2020	515.5	$ 1.0	$ (184.0)	714.1	(15.9)	(28.8)	486.4	29.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(1.4)					(2.7)	(2.7)	1.3
Reclassifications of prior service benefit and actuarial benefit amortization to earnings, net of tax	0.1				0.1		0.1
Currency translation adjustment	(0.4)				(0.4)		(0.4)
Share-based compensation expense	0.6			0.6			0.6
Simplification Transaction:
Dividends	(5.1)					(5.1)	(5.1)
Ending balance, shares at Sep. 30, 2020		98,172,557	15,404,482
Ending balance at Sep. 30, 2020	$ 509.3	$ 1.0	$ (184.0)	$ 714.7	$ (16.2)	$ (36.6)	$ 478.9	$ 30.4