Supplementary Cash Flow Information (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Supplemental cash flow, net cash paid (received) during the period for: [Abstract]
Interest, net of capitalized interest	$ 102.4	$ 100.7
Income taxes	(9.4)	(5.7)
Net Cash Provided by (Used in) Operating Activities	192.5	249.9
Cash and cash equivalents	30.8		$ 48.6
Supplemental cash flow, noncash investing and financing activities [Abstract]
Capital investments	24.2	25.6
Restricted Stock and Restricted Stock Units [Member]
Supplemental cash flow, noncash investing and financing activities [Abstract]
Issuance of restricted stock and restricted stock units	2.9	4.3
SunCoke Middletown [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Supplemental cash flow, net cash paid (received) during the period for: [Abstract]
Net Cash Provided by (Used in) Operating Activities	54.8	$ 60.4
Cash and cash equivalents	$ 1.2		$ 1.1

Net cash paid during the period for: [Abstract]

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Future cash outflow to pay for purchases of fixed assets that have occurred.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.

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Amount of cash paid for interest, excluding capitalized interest, classified as operating activity. Includes, but is not limited to, payment to settle zero-coupon bond for accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.

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Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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The fair value of stock issued in noncash financing activities.

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