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Property, Plant, Equipment and Mine Development - (Details) - USD ($)
Dec. 31, 2023
Dec. 31, 2022
Property, Plant, Equipment and Mine Development[Line Items]    
Less: Accumulated depreciation, depletion and amortization $ (2,066,300,000) $ (1,787,000,000)
Property, plant, equipment and mine development, net 2,844,100,000 2,865,000,000
Coal reserves 1,200,000,000 1,300,000,000
Coal reserves not subject to depletion 100,000,000 100,000,000
Miscellaneous Receivables    
Property, Plant, Equipment and Mine Development[Line Items]    
Accounts receivable, allowance for credit losses 700,000,000 700,000,000
Land and coal interests    
Property, Plant, Equipment and Mine Development[Line Items]    
Property, plant equipment and mine development, gross 2,475,200,000 2,514,700,000
Buildings and improvements    
Property, Plant, Equipment and Mine Development[Line Items]    
Property, plant equipment and mine development, gross 647,600,000 594,200,000
Machinery and equipment    
Property, Plant, Equipment and Mine Development[Line Items]    
Property, plant equipment and mine development, gross 1,787,600,000 1,543,100,000
Coal Reserves Held by Fee Ownership    
Property, Plant, Equipment and Mine Development[Line Items]    
Coal reserves $ 500,000,000 $ 600,000,000