UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Revenues	$ 651.3	$ 846.2
Costs and expenses
Operating costs and expenses (exclusive of items shown separately below)	582.6	779.5
Depreciation, depletion and amortization	68.3	106.0
Asset retirement obligation expenses	15.9	17.6
Selling and administrative expenses	21.7	24.9
Restructuring charges	2.1	6.5
Transaction costs related to joint ventures	0.0	4.2
Other operating (income) loss:
Net loss (gain) on disposals	0.6	(8.1)
Loss from equity affiliates	0.9	9.1
Operating loss	(40.8)	(93.5)
Interest expense	52.4	33.1
Gain on early debt extinguishment	(3.5)	0.0
Interest income	(1.5)	(3.1)
Net periodic benefit (credit) costs, excluding service cost	(8.7)	2.8
Loss from continuing operations before income taxes	(79.5)	(126.3)
Income tax (benefit) provision	(1.8)	3.0
Loss from continuing operations, net of income taxes	(77.7)	(129.3)
Loss from discontinued operations, net of income taxes	(2.0)	(2.2)
Net loss	(79.7)	(131.5)
Less: Net income (loss) attributable to noncontrolling interests	0.4	(1.8)
Net loss attributable to common stockholders	$ (80.1)	$ (129.7)
Loss from continuing operations:
Basic loss per share	$ (0.79)	$ (1.31)
Diluted loss per share	(0.79)	(1.31)
Net loss attributable to common stockholders:
Basic loss per share	(0.81)	(1.33)
Diluted loss per share	$ (0.81)	$ (1.33)