Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Supplemental cash flow, net cash paid (received) during the period for: [Abstract]
Interest, net of capitalized interest	$ 87.4	$ 62.9
Income taxes	0.2	(0.5)
Net Cash Provided by (Used in) Operating Activities	200.1	(380.6)
Cash and Cash Equivalents, at Carrying Value	90.0	60.8	$ 70.2	$ 45.3
Supplemental cash flow, noncash investing and financing activities [Abstract]
Capital investments	26.1	7.6
Restricted Stock and Restricted Stock Units [Member]
Supplemental cash flow, noncash investing and financing activities [Abstract]
Issuance of restricted stock and restricted stock units	4.1	4.0
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	68.2	$ 43.8
Cash and Cash Equivalents, at Carrying Value	$ 15.9		$ 18.2