Other Events (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Commercial Events [Line Items]
Interest in unincorporated joint venture project		50.00%
Contribution to construction and development of joint venture		$ 59.0	$ 72.0
Gain on formation of United Wambo Joint Venture		0.0	0.0	$ (48.1)
Revenues		3,318.3	2,881.1	4,623.4
Provision for equipment loss		0.0	0.0	83.2	$ 66.4
Insurance recovery		0.0	0.0	125.0
Proceeds from disposal of assets, net of receivables		17.8	27.1	30.0
Gain on disposition of assets		31.5	15.2	2.1
Mine Reclamation and Closing Liability, Noncurrent		9.4
Restructuring charges		8.3	37.9	24.3
North Goonyella Mine
Other Commercial Events [Line Items]
Costs related to north goonyella events				111.5
Containment and idling costs		13.0	32.3
Insurance recovery	$ 125.0		$ 125.0
North Goonyella Mine | Mine Carrying Value
Other Commercial Events [Line Items]
Costs related to north goonyella events				$ 300.0
Millennium Mine
Other Commercial Events [Line Items]
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax		26.1
Wilkie Creek Mine
Other Commercial Events [Line Items]
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax		$ 24.6