UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Revenue	$ 1,321.9	$ 723.4	$ 2,013.3	$ 1,374.7
Costs and expenses
Operating costs and expenses (exclusive of items shown separately below)	825.6	611.4	1,524.6	1,194.0
Depreciation, depletion and amortization	73.8	77.1	146.7	145.4
Asset retirement obligation expenses	12.7	15.1	27.7	31.0
Selling and administrative expenses	21.8	21.4	44.9	43.1
Restructuring charges	0.2	2.1	1.8	4.2
Other operating (income) loss:
Net gain on disposals	(12.8)	(3.0)	(17.7)	(2.4)
(Income) loss from equity affiliates	(48.7)	3.5	(93.4)	4.4
Operating profit (loss)	449.3	(4.2)	378.7	(45.0)
Interest expense	37.6	45.4	77.0	97.8
Net loss (gain) on early debt extinguishment	(2.3)	(11.8)	(25.8)	15.3
Interest income	(0.9)	(1.3)	(1.4)	(2.8)
Net periodic benefit credit, excluding service cost	(12.3)	(8.7)	(24.5)	(17.4)
Income (loss) from continuing operations before income taxes	422.6	(27.8)	301.8	(107.3)
Income tax provision (benefit)	11.3	(4.8)	10.3	(6.6)
Income (loss) from continuing operations, net of income taxes	411.3	(23.0)	291.5	(100.7)
Loss from discontinued operations, net of income taxes	(0.7)	(2.3)	(1.5)	(4.3)
Net income (loss)	410.6	(25.3)	290.0	(105.0)
Less: Net income attributable to noncontrolling interests	1.1	3.3	0.0	3.7
Net income (loss) attributable to common stockholders	$ 409.5	$ (28.6)	$ 290.0	$ (108.7)
Income (loss) from continuing operations:
Basic income (loss) per share	$ 2.85	$ (0.26)	$ 2.08	$ (1.05)
Diluted income (loss) per share	2.55	(0.26)	1.93	(1.05)
Net income (loss) attributable to common stockholders:
Basic income (loss) per share	2.84	(0.28)	2.07	(1.09)
Diluted income (loss) per share	$ 2.54	$ (0.28)	$ 1.93	$ (1.09)