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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Share-Based Compensation - Schedule of Compensation Expense, Unrecognized Compensation Costs, and Unrecognized Compensation Cost is Expected to be Recognized (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Total equity awards \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	$ 1.3	$ 1.5	$ 1.7	$ 2.9
RSUs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized Compensation Cost	2.5		$ 2.5
Weighted Average Remaining Recognition Period			2 years 1 month 6 days
RSUs \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	1.1	1.4	$ 1.3	1.8
PSUs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized Compensation Cost	1.3		$ 1.3
Weighted Average Remaining Recognition Period			2 years 2 months 12 days
PSUs \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	0.2	0.1	$ 0.4	1.1
Total liability awards \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	0.6	0.7	1.1	2.1
Cash RSUs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized Compensation Cost	1.6		$ 1.6
Weighted Average Remaining Recognition Period			1 year 7 months 6 days
Cash RSUs \| Selling, General and Administrative Expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	0.3	0.3	$ 0.3	0.8
Cash incentive award \| Suncoke LTCIP
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized Compensation Cost	2.5		$ 2.5
Weighted Average Remaining Recognition Period			2 years
Cash incentive award \| Selling, General and Administrative Expenses \| Suncoke LTCIP
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Compensation expense	$ 0.3	$ 0.4	$ 0.8	$ 1.3