Supplemental Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Supplemental cash flow, net cash paid (received) during the period for: [Abstract]
Interest, net of capitalized interest	$ 57.8	$ 27.8
Income taxes	1.0	0.1
Net Cash Provided by (Used in) Operating Activities	(104.5)	(310.1)
Cash and Cash Equivalents, at Carrying Value	58.4	37.4	227.0	42.0
Supplemental cash flow, noncash investing and financing activities [Abstract]
Capital investments	5.6	8.8
Restricted Stock and Restricted Stock Units [Member]
Supplemental cash flow, noncash investing and financing activities [Abstract]
Issuance of restricted stock and restricted stock units	2.5	5.0
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	39.8	30.4
Cash and Cash Equivalents, at Carrying Value	$ 10.8		$ 0