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Share-Based Compensation - Compensation Expense and Unrecognized Compensation Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
RSUs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized Compensation Cost	$ 1.1		$ 1.1
Weighted Average Remaining Recognition Period			1 year
RSUs \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	0.6	$ 0.7	$ 1.6	$ 1.7
PSUs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized Compensation Cost	1.5		$ 1.5
Weighted Average Remaining Recognition Period			1 year 1 month 6 days
PSUs \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	1.2	1.2	$ 3.0	2.4
Total equity awards \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	1.8	1.9	4.6	4.1
Cash RSUs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized Compensation Cost	1.4		$ 1.4
Weighted Average Remaining Recognition Period			1 year 10 months 24 days
Cash RSUs \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	0.1	0.2	$ 1.0	1.3
Cash incentive award \| Suncoke LTCIP
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized Compensation Cost	3.1		$ 3.1
Weighted Average Remaining Recognition Period			1 year 4 months 24 days
Cash incentive award \| Selling, General and Administrative Expenses \| Suncoke LTCIP
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	1.5	1.1	$ 3.9	2.4
Total liability awards \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	$ 1.6	$ 1.3	$ 4.9	$ 3.7