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Property, Plant, Equipment and Mine Development (Tables)
3 Months Ended
Mar. 31, 2022
Property, Plant and Equipment [Abstract]  
Schedule of Property, Plant, Equipment and Mine Development
The composition of property, plant, equipment and mine development, net, as of March 31, 2022 and December 31, 2021 is set forth in the table below:
March 31, 2022December 31, 2021
(Dollars in millions)
Land and coal interests$2,494.1 $2,494.1 
Buildings and improvements590.2 550.8 
Machinery and equipment1,370.9 1,386.2 
Less: Accumulated depreciation, depletion and amortization(1,551.9)(1,480.5)
Property, plant, equipment and mine development, net$2,903.3 $2,950.6