Segment and Geographic Information - Segment Results (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 4,981.9	$ 3,318.3	$ 2,881.1
Adjusted EBITDA	1,844.7	916.7	258.8
Additions to property, plant, equipment and mine development	221.5	183.1	191.4
(Income) loss from equity affiliates	(131.2)	(82.1)	60.1
Seaborne Thermal Mining
Segment Reporting Information [Line Items]
Revenues	1,345.6	934.0	711.8
Adjusted EBITDA	647.6	353.1	163.2
Additions to property, plant, equipment and mine development	38.8	88.6	100.7
(Income) loss from equity affiliates	0.0	0.0	0.0
Seaborne Metallurgical Mining
Segment Reporting Information [Line Items]
Revenues	1,616.9	727.7	486.5
Adjusted EBITDA	781.7	178.2	(130.2)
Additions to property, plant, equipment and mine development	84.8	25.1	50.8
(Income) loss from equity affiliates	0.0	0.0	0.0
Powder River Basin Mining
Segment Reporting Information [Line Items]
Revenues	1,065.5	971.2	991.1
Adjusted EBITDA	68.2	134.9	194.8
Additions to property, plant, equipment and mine development	59.1	41.4	13.2
(Income) loss from equity affiliates	0.0	0.0	0.0
Other U.S. Thermal Mining
Segment Reporting Information [Line Items]
Revenues	952.2	689.1	707.3
Adjusted EBITDA	242.4	164.2	168.4
Additions to property, plant, equipment and mine development	35.3	24.2	23.3
(Income) loss from equity affiliates	0.0	0.0	0.0
Corporate and Other (1)
Segment Reporting Information [Line Items]
Revenues	1.7	(3.7)	(15.6)
Adjusted EBITDA	104.8	86.3	(137.4)
Additions to property, plant, equipment and mine development	3.5	3.8	3.4
(Income) loss from equity affiliates	$ (131.2)	$ (82.1)	$ 60.1