Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Supplemental cash flow, net cash paid (received) during the period for: [Abstract]
Interest, net of capitalized interest	$ 4.8	$ 5.1
Income taxes	(3.4)	0.0
Net Cash Provided by (Used in) Operating Activities	136.7	(2.7)
Cash and Cash Equivalents, at Carrying Value	113.0	89.4	$ 56.6	$ 70.2
Supplemental cash flow, noncash investing and financing activities [Abstract]
Capital investments	24.5	18.1
Restricted Stock and Restricted Stock Units [Member]
Supplemental cash flow, noncash investing and financing activities [Abstract]
Issuance of restricted stock and restricted stock units	1.4	3.4
Variable Interest Entity, Primary Beneficiary [Member] | SunCoke Middletown [Member]
Supplemental cash flow, net cash paid (received) during the period for: [Abstract]
Net Cash Provided by (Used in) Operating Activities	20.4	29.0
Cash and Cash Equivalents, at Carrying Value	7.0		$ 7.6
Research And Innovation Center Middletown OH [Member]
Supplemental cash flow, noncash investing and financing activities [Abstract]
Research and Innovation Center capital lease	$ 9.6	$ 0.0