Segment Information - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reportable segment results
Revenues	$ 1,078.9	$ 1,342.5	$ 3,711.7	$ 3,355.8
Adjusted EBITDA	270.0	438.9	1,018.8	1,344.2
Seaborne Thermal
Reportable segment results
Revenues	297.4	353.2	1,043.4	959.3
Adjusted EBITDA	115.5	171.2	477.0	438.5
Seaborne Metallurgical
Reportable segment results
Revenues	247.0	310.7	907.9	1,165.8
Adjusted EBITDA	78.6	113.2	271.9	593.9
Powder River Basin
Reportable segment results
Revenues	313.0	290.5	878.0	771.4
Adjusted EBITDA	54.1	37.9	116.1	43.5
Other U.S. Thermal
Reportable segment results
Revenues	228.2	261.4	677.5	689.4
Adjusted EBITDA	49.1	72.7	165.2	184.6
Corporate and Other (1)
Reportable segment results
Revenues	(6.7)	126.7	204.9	(230.1)
Adjusted EBITDA	$ (27.3)	$ 43.9	$ (11.4)	$ 83.7