Segment Information - Segment Results (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reportable segment results
Revenue	$ 691.4	$ 651.3
Adjusted EBITDA	327.5	61.1
Seaborne Thermal Mining
Reportable segment results
Revenue	251.2	176.4
Adjusted EBITDA	90.5	28.5
Seaborne Metallurgical Mining
Reportable segment results
Revenue	321.3	87.5
Adjusted EBITDA	181.0	(22.4)
Powder River Basin Mining
Reportable segment results
Revenue	251.2	228.4
Adjusted EBITDA	7.6	30.1
Other U.S. Thermal Mining
Reportable segment results
Revenue	203.1	149.3
Adjusted EBITDA	50.0	36.2
Corporate and Other (1)
Reportable segment results
Revenue	(335.4)	9.7
Adjusted EBITDA	$ (1.6)	$ (11.3)