UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Revenue	$ 691.4	$ 651.3
Costs and expenses
Operating costs and expenses (exclusive of items shown separately below)	699.0	582.6
Depreciation, depletion and amortization	72.9	68.3
Asset retirement obligation expenses	15.0	15.9
Selling and administrative expenses	23.1	21.7
Restructuring charges	1.6	2.1
Other operating (income) loss:
Net (gain) loss on disposals	(4.9)	0.6
(Income) loss from equity affiliates	(44.7)	0.9
Operating loss	(70.6)	(40.8)
Interest expense	39.4	52.4
Net loss (gain) on early debt extinguishment	23.5	(3.5)
Interest income	(0.5)	(1.5)
Net periodic benefit credit, excluding service cost	(12.2)	(8.7)
Loss from continuing operations before income taxes	(120.8)	(79.5)
Income tax benefit	(1.0)	(1.8)
Loss from continuing operations, net of income taxes	(119.8)	(77.7)
Loss from discontinued operations, net of income taxes	(0.8)	(2.0)
Net loss	(120.6)	(79.7)
Less: Net (loss) income attributable to noncontrolling interests	(1.1)	0.4
Net loss attributable to common stockholders	$ (119.5)	$ (80.1)
Loss from continuing operations:
Basic loss per share	$ (0.87)	$ (0.79)
Diluted loss per share	(0.87)	(0.79)
Net loss attributable to common stockholders:
Basic loss per share	(0.88)	(0.81)
Diluted loss per share	$ (0.88)	$ (0.81)