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Summary of Significant Accounting Policies (Tables)
12 Months Ended
Dec. 31, 2025
Accounting Policies [Abstract]  
Property, Plant and Equipment estimated useful lives of the building and improvements and machinery and equipment asset categories range from 1 to 31 years. The estimated life of leasehold improvements is the shorter of useful life or remaining life of the lease.
Property, plant, equipment and mine development, net, as of December 31, 2025 and 2024 consisted of the following:
December 31,
20252024
(Dollars in millions)
Land and coal interests$2,691.2 $2,648.5 
Buildings and improvements758.8 726.7 
Machinery and equipment2,377.1 2,078.8 
Less: Accumulated depreciation, depletion and amortization(2,673.8)(2,372.5)
Property, plant, equipment and mine development, net$3,153.3 $3,081.5