Other Events Narrative (Details) $ in Millions, $ in Millions		1 Months Ended	3 Months Ended			6 Months Ended
	Jul. 05, 2023 USD ($)	Jul. 28, 2023 USD ($) shares	Jun. 30, 2023 USD ($) shares	Jun. 30, 2023 AUD ($) shares	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)
Other Commercial Events [Line Items]
Revenues			$ 1,268.8		$ 1,321.9	$ 2,632.8	$ 2,013.3
Other Noncash Income			9.3		0.0	9.2
Revenue from Collaborative Arrangement, Excluding Revenue from Contract with Customer				$ 30.0
Revenue related to excess port and rail capacity agreement			19.2
Provision for Other Losses			28.7			28.7
Storm Damage Provision			5.0			5.0
Storm damage provision for materials and supplies inventories			4.0			4.0
Storm damage provision for buildings and equipment			$ 1.0			1.0
Common stock, shares, acquired | shares			8,900,000	8,900,000
Common stock repurchase amount including commission fees			$ 184.2
Provision for other losses related to longwall development and other costs			17.8			17.8
Provision for other losses for equipment			10.9			10.9
Subsequent Event
Other Commercial Events [Line Items]
Common stock, shares, acquired | shares		3,100,000
Common stock repurchase amount including commission fees	$ 11.2	$ 67.0
Treasury Stock, Common
Other Commercial Events [Line Items]
Sales and Excise Tax Payable			$ 1.6		$ 0.0	$ 1.6	$ 0.0