Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Trade Receivables, net
Allowance for doubtful receivables	$ (0.8)	$ (0.8)
Trade receivables, net	332.7	112.8
Inventories
Finished products	90.3	37.2
Work-in-process	162.2	46.0
Raw materials	143.0	62.3
Operating supplies	9.1	6.5
Total	404.6	152.0
Property, Plant and Equipment, net
Land and improvements	26.0	21.5
Buildings and leasehold improvements	179.0	117.2
Machinery and equipment	1,151.5	847.4
Construction in progress	75.3	37.8
Property, plant and equipment, gross	1,431.8	1,023.9
Accumulated depreciation and amortization	(480.4)	(398.4)
Assets held for sale	3.8	1.7
Property, plant and equipment, net	955.2	627.2
Other Accrued Liabilities
Uncleared cash disbursements	10.9	2.1
Accrued income taxes and other taxes payable	9.5	5.2
Accrued annual contribution to Salaried VEBA		1.7
Accrued interest	9.9	11.6
Short-term environmental accrual	2.6	3.7
Other	25.5	17.1
Total	58.4	41.4
Long-Term Liabilities
Workers' compensation accruals	31.9	30.6
Long-term environmental accrual	14.2	15.1
Other long-term liabilities	26.4	31.6
Total	72.5	77.3
Billed
Trade Receivables, net
Billed trade receivables	$ 333.5	$ 113.6