CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenues	$ 3,318.3	$ 2,881.1	$ 4,623.4
Costs and expenses
Operating costs and expenses (exclusive of items shown separately below)	2,553.1	2,524.9	3,536.6
Depreciation, depletion and amortization	308.7	346.0	601.0
Asset retirement obligation expenses	44.7	45.7	58.4
Selling and administrative expenses	84.9	99.5	145.0
Restructuring charges	8.3	37.9	24.3
Transaction costs related to joint ventures	0.0	23.1	21.6
Other operating (income) loss:
Net gain on disposals	(31.5)	(15.2)	(2.1)
Gain on formation of United Wambo Joint Venture	0.0	0.0	(48.1)
Asset impairment	0.0	1,487.4	270.2
Provision for North Goonyella equipment loss	0.0	0.0	83.2
North Goonyella insurance recovery	0.0	0.0	(125.0)
(Income) loss from equity affiliates	(82.1)	60.1	(3.4)
Operating profit (loss)	432.2	(1,728.3)	61.7
Interest expense	183.4	139.8	144.0
Net (gain) loss on early debt extinguishment	33.2	0.0	(0.2)
Interest income	(6.5)	(9.4)	(27.0)
Net periodic benefit (credit) costs, excluding service cost	(38.3)	(1.8)	19.4
Net mark-to-market adjustment on actuarially determined liabilities	(43.4)	(5.1)	67.4
Income (loss) from continuing operations before income taxes	370.2	(1,851.8)	(142.3)
Income tax provision	22.8	8.0	46.0
Income (loss) from continuing operations, net of income taxes	347.4	(1,859.8)	(188.3)
Income (loss) from discontinued operations, net of income taxes	24.0	(14.0)	3.2
Net income (loss)	371.4	(1,873.8)	(185.1)
Less: Net income (loss) attributable to noncontrolling interests	11.3	(3.5)	26.2
Net income (loss) attributable to common stockholders	$ 360.1	$ (1,870.3)	$ (211.3)
Income (loss) from continuing operations:
Basic income (loss) per share	$ 3.03	$ (18.99)	$ (2.07)
Diluted income (loss) per share	3.00	(18.99)	(2.07)
Net income (loss) attributable to common stockholders:
Basic income (loss) per share	3.24	(19.14)	(2.04)
Diluted income (loss) per share	$ 3.22	$ (19.14)	$ (2.04)