v3.26.1
Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Jun. 30, 2025
Trade Receivables, Net      
Accounts receivable $ 575.6 $ 423.9  
Allowance for doubtful receivables (0.6) (0.6)  
Receivables, net 575.0 423.3  
Inventories      
Finished products 145.7 156.1  
Work-in-process 364.7 316.7  
Raw materials 321.8 236.2  
Operating supplies 15.9 16.2  
Inventories 848.1 725.2  
Property, Plant and Equipment, Net      
Land and improvements 45.8 38.2  
Buildings and leasehold improvements 306.4 302.6  
Machinery and equipment 1,610.3 1,586.7  
Construction in progress 84.6 66.7  
Property, plant and equipment, gross 2,047.1 1,994.2  
Accumulated depreciation and amortization (903.4) (849.1)  
Land held for sale 0.0 0.1  
Property, plant and equipment, net 1,143.7 1,145.2  
Other Assets      
Restricted cash - Note 11 19.9 19.9 $ 19.8
Long-term replacement parts 34.0 28.5  
Net assets of Salaried VEBA 10.0 9.7  
Other 19.4 17.6  
Other assets 83.3 75.7  
Other Accrued Liabilities      
Uncleared cash disbursements 0.5 45.8  
Accrued income taxes and other taxes payable 8.5 7.8  
Accrued annual contribution to Salaried VEBA 0.0 2.9  
Accrued interest 12.0 6.9  
Current operating lease liabilities 5.7 4.8  
Current finance lease liabilities 3.5 2.3  
Current deferred compensation plan liabilities - Note 3 1.3 1.2  
Other - Note 4 49.6 19.6  
Other accrued liabilities 81.1 91.3  
Long-Term Liabilities      
Workers' compensation accrual 25.9 26.0  
Long-term environmental accrual - Note 6 16.7 17.4  
Other long-term liabilities 42.7 38.0  
Long-term liabilities $ 85.3 $ 81.4