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Inventories (Tables)
12 Months Ended
Dec. 31, 2020
Inventory Disclosure [Abstract]  
Components of inventories These components of inventories were as follows:
 December 31,
 20202019
 (Dollars in millions)
Coal$60.6 $94.4 
Coke21.1 8.1 
Materials, supplies and other44.9 44.5 
Total inventories$126.6 $147.0