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Inventories (Tables)
12 Months Ended
Dec. 31, 2020
Inventory Disclosure [Abstract]  
Inventories
Inventories as of December 31, 2020 and December 31, 2019 consisted of the following:
December 31,
 20202019
 (Dollars in millions)
Materials and supplies$102.6 $116.3 
Raw coal70.5 85.1 
Saleable coal88.5 130.1 
Inventories$261.6 $331.5