Partnership Initial Public Offering and Dropdown Transactions - Effects of Changes in Company's Ownership (Details) - USD ($) $ in Millions			3 Months Ended								12 Months Ended
	Aug. 12, 2015	Jan. 13, 2015	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	May. 09, 2014
Business Acquisition [Line Items]
Net income attributable to SunCoke Energy, Inc.			$ 19.0	$ (23.5)	$ (13.5)	$ (4.0)	$ (65.5)	$ (3.6)	$ (49.2)	$ (7.8)	$ (22.0)	$ (126.1)	$ 25.0
Decrease in noncontrolling interest											75.0	0.0
Increase in SunCoke Energy, Inc. equity for the contribution of 33 percent interest in Haverhill and Middletown											12.8
Change from net loss attributable to SunCoke Energy, Inc. and dropdown transactions											(30.0)	(42.4)
Haverhill Coke Company LLC and Middletown Coke Company LLC
Business Acquisition [Line Items]
Increase in SunCoke Energy, Inc. equity for the contribution of 33 percent interest in Haverhill and Middletown									$ 83.7		0.0	83.7
Interest acquired (as a percent)														33.00%
Gateway Energy and Coal Company, LLC
Business Acquisition [Line Items]
Interest acquired (as a percent)	23.00%	75.00%
Granite City
Business Acquisition [Line Items]
Decrease in noncontrolling interest											(6.5)	0.0
Decrease in SunCoke Energy, Inc. for the contribution of an additional 23 percent interest in Granite City											$ (1.5)	$ 0.0
SunCoke Energy Partners, L.P. | Haverhill Coke Company LLC and Middletown Coke Company LLC
Business Acquisition [Line Items]
Interest acquired (as a percent)														33.00%
SunCoke Energy Partners, L.P. | Gateway Energy and Coal Company, LLC
Business Acquisition [Line Items]
Decrease in noncontrolling interest	$ 1.5
SunCoke Energy Partners, L.P. | Granite City
Business Acquisition [Line Items]
Decrease in noncontrolling interest		$ 6.5
Interest acquired (as a percent)		75.00%