UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Income Statement [Abstract]
Revenues	$ (1,268.8)	$ (1,321.9)	$ (2,632.8)	$ (2,013.3)
Costs and expenses
Operating costs and expenses (exclusive of items shown separately below)	862.0	825.6	1,708.6	1,524.6
Depreciation, depletion and amortization	80.6	73.8	156.9	146.7
Asset retirement obligation expenses	15.5	12.7	30.9	27.7
Selling and administrative expenses	21.7	21.8	44.5	44.9
Restructuring charges	2.0	0.2	2.1	1.8
Other operating income:
Net gain on disposals	(5.2)	(12.8)	(7.1)	(17.7)
Asset impairment	0.0	0.0	2.0	0.0
Provision for NARM and Shoal Creek loss	33.7	0.0	33.7	0.0
Income from equity affiliates	(2.3)	(48.7)	(4.1)	(93.4)
Operating profit	260.8	449.3	665.3	378.7
Interest expense	13.3	37.6	31.7	77.0
Net loss on early debt extinguishment	2.0	2.3	8.8	25.8
Interest income	(23.1)	(0.9)	(36.2)	(1.4)
Net periodic benefit credit, excluding service cost	(9.7)	(12.3)	(19.4)	(24.5)
Income from continuing operations before income taxes	278.3	422.6	680.4	301.8
Income tax provision	74.2	11.3	192.2	10.3
Income from continuing operations, net of income taxes	204.1	411.3	488.2	291.5
Loss from discontinued operations, net of income taxes	(1.3)	(0.7)	(2.6)	(1.5)
Net income	202.8	410.6	485.6	290.0
Less: Net income attributable to noncontrolling interests	23.6	1.1	37.9	0.0
Net income attributable to common stockholders	$ 179.2	$ 409.5	$ 447.7	$ 290.0
Income from continuing operations:
Basic income per share	$ 1.27	$ 2.85	$ 3.14	$ 2.08
Diluted income per share	1.16	2.55	2.85	1.93
Net income attributable to common stockholders:
Basic income per share	1.26	2.84	3.12	2.07
Diluted income per share	$ 1.15	$ 2.54	$ 2.83	$ 1.93