Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 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	$ 82.4	$ 59.1
Income taxes	0.1	0.4
Net Cash Provided by (Used in) Operating Activities	83.9	(331.1)
Cash and Cash Equivalents, at Carrying Value	75.0	54.8	$ 70.2	$ 45.3
Supplemental cash flow, noncash investing and financing activities [Abstract]
Capital investments	24.3	6.6
Restricted Stock and Restricted Stock Units [Member]
Supplemental cash flow, noncash investing and financing activities [Abstract]
Issuance of restricted stock and restricted stock units	3.8	3.7
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	46.1	$ 32.6
Cash and Cash Equivalents, at Carrying Value	$ 21.0		$ 18.2