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Inventories (Details) - USD ($)
$ in Millions
Sep. 30, 2021
Dec. 31, 2020
Inventory, Net [Abstract]    
Raw materials $ 95.3 $ 95.9
Work-in-process 55.4 40.5
Finished goods 26.4 26.9
Operating and other supplies 166.2 127.8
Total inventories $ 343.3 $ 291.1