Segment and Geographic Information - Reconciliation of Consolidated Income (Loss), Net of Income Taxes to Adjusted EBITDA (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income (loss) from continuing operations, net of income taxes		$ 347.4	$ (1,859.8)	$ (188.3)
Depreciation, depletion and amortization		308.7	346.0	601.0
Asset retirement obligation expenses		44.7	45.7	58.4
Restructuring charges		8.3	37.9	24.3
Transaction costs related to joint ventures		0.0	23.1	21.6
Gain on formation of United Wambo Joint Venture		0.0	0.0	(48.1)
Asset impairment		0.0	1,487.4	270.2
Provision for North Goonyella equipment loss		0.0	0.0	83.2	$ 66.4
North Goonyella insurance recovery - equipment		0.0	0.0	(91.1)
Changes in deferred tax asset valuation allowance and reserves and amortization of basis difference related to equity affiliates		(33.8)	30.9	(18.8)
Interest expense		183.4	139.8	144.0
Net (gain) loss on early debt extinguishment		(33.2)	0.0	0.2
Interest income		(6.5)	(9.4)	(27.0)
Net mark-to-market adjustment on actuarially determined liabilities		(43.4)	(5.1)	67.4
Unrealized losses (gains) on derivative contracts related to forecasted sales		115.1	29.6	(42.2)
Unrealized losses (gains) on foreign currency option contracts		7.5	(7.1)	(1.2)
Take-or-pay contract-based intangible recognition		(4.3)	(8.2)	(16.6)
Income tax provision		22.8	8.0	46.0
Total Adjusted EBITDA		916.7	258.8	883.0
Insurance recovery		$ 0.0	0.0	125.0
North Goonyella Mine
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Insurance recovery	$ 125.0		125.0
Provision for equipment loss excluded from EBITDA			24.7	$ 66.4
Business Interruption Losses			$ 33.9