Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Supplemental cash flow, net cash paid (received) during the period for: [Abstract]
Interest, net of capitalized interest	$ 45.1	$ 4.8
Income taxes	0.1	(3.4)
Net Cash Provided by (Used in) Operating Activities	36.3	136.7
Cash and Cash Equivalents, at Carrying Value	185.7	113.0	$ 173.2	$ 56.6
Supplemental cash flow, noncash investing and financing activities [Abstract]
Capital investments	21.6	21.2
Restricted Stock and Restricted Stock Units [Member]
Supplemental cash flow, noncash investing and financing activities [Abstract]
Issuance of performance shars, restricted stock and restricted stock units	3.8	1.4
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	20.3	20.4
Cash and Cash Equivalents, at Carrying Value	10.1		$ 5.0
Research And Innovation Center Middletown OH [Member]
Supplemental cash flow, noncash investing and financing activities [Abstract]
Research and Innovation Center capital lease	$ 0.0	$ 9.6