Property, Plant, Equipment and Mine Development - (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021
Property, Plant, Equipment and Mine Development[Line Items]
Less: Accumulated depreciation, depletion and amortization	$ (1,787,000,000)	$ (1,480,500,000)
Property, plant, equipment and mine development, net	2,865,000,000	2,950,600,000
Coal reserves	1,300,000,000	1,400,000,000
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	2,514,700,000	2,494,100,000
Buildings and improvements
Property, Plant, Equipment and Mine Development[Line Items]
Property, plant equipment and mine development, gross	594,200,000	550,800,000
Machinery and equipment
Property, Plant, Equipment and Mine Development[Line Items]
Property, plant equipment and mine development, gross	$ 1,543,100,000	1,386,200,000
Coal Reserves Held by Fee Ownership
Property, Plant, Equipment and Mine Development[Line Items]
Coal reserves		$ 600,000,000