Share-Based Compensation (Compensation Expense and Unrecognized Compensation Costs) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 0.5
Recognition Period	1 year 7 months 6 days
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 0.3
Recognition Period	1 year 8 months 12 days
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 2.6
Recognition Period	1 year 10 months 24 days
Restricted Stock Units Settled in Cash
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 0.7
Recognition Period	1 year 4 months 24 days
Suncoke LTCIP \| Cash Incentive Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Cost	$ 0.9
Recognition Period	1 year 9 months 18 days
Selling, General and Administrative Expenses \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 0.5	$ 1.3	$ 2.1
Net of tax	0.4	0.8	1.3
Selling, General and Administrative Expenses \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	0.4	1.1	2.6
Net of tax	0.3	0.7	1.7
Selling, General and Administrative Expenses \| Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	1.9	1.9	1.4
Net of tax	1.7	1.2	0.9
Selling, General and Administrative Expenses \| Equity Classified Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	2.8	4.3	6.1
Net of tax	2.4	2.7	3.9
Selling, General and Administrative Expenses \| Restricted Stock Units Settled in Cash
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	0.8	1.0	0.7
Net of tax	0.6	0.6	0.5
Selling, General and Administrative Expenses \| Suncoke LTCIP \| Cash Incentive Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	0.9	0.2	0.1
Net of tax	0.7	0.1	0.1
Selling, General and Administrative Expenses \| Suncoke LTCIP \| Liability Classified Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	1.7	1.2	0.8
Net of tax	$ 1.3	$ 0.7	$ 0.6

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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- Definition

The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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