Segment Information - Reconciliation to Adjusted EBITDA (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Loss from continuing operations, net of income taxes	$ (59.6)	$ (64.8)	$ (160.3)	$ (1,739.4)
Depreciation, depletion and amortization	77.9	72.2	223.3	266.5
Asset retirement obligation expenses	14.3	14.3	45.3	46.0
Restructuring charges	1.7	8.1	5.9	31.1
Transaction costs related to joint ventures	0.0	6.0	0.0	23.1
Asset impairment	0.0	0.0	0.0	1,418.1
Changes in deferred tax asset valuation allowance and reserves and amortization of basis difference related to equity affiliates	(6.4)	(0.5)	(8.4)	(1.6)
Interest expense	45.5	34.9	143.3	102.3
Net gain on early debt extinguishment	(16.0)	0.0	(31.3)	0.0
Interest income	(1.4)	(1.6)	(4.2)	(7.1)
Defined Benefit Plan, Net Mark-To-Market Adjustment on Actuarially Determined Liabilities	0.0	13.0	0.0	13.0
Unrealized losses on derivative contracts related to forecasted sales	238.4	16.1	264.0	11.3
Unrealized (gains) losses on foreign currency option contracts	(0.6)	(0.7)	8.2	(3.6)
Take-or-pay contract-based intangible recognition	(1.0)	(1.5)	(3.2)	(6.8)
Income tax (benefit) provision	(3.7)	(0.1)	(10.3)	2.7
Adjusted EBITDA	$ 289.1	$ 95.4	$ 472.3	$ 155.6