Unaudited Condensed Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash Flows From Operating Activities
Net (loss) income	$ (1,679,100,000)	$ 169,400,000
Loss from discontinued operations, net of income taxes	4,500,000	6,800,000
(Loss) income from continuing operations, net of income taxes	(1,674,600,000)	176,200,000
Adjustments to reconcile (loss) income from continuing operations, net of income taxes to net cash (used in) provided by operating activities:
Depreciation, depletion and amortization	194,300,000	337,900,000
Noncash interest expense, net	8,000,000.0	11,100,000
Deferred income taxes	(500,000)	(300,000)
Noncash share-based compensation	6,100,000	21,600,000
Asset impairment	1,418,100,000	0
Net gain on disposals	(7,900,000)	(1,700,000)
Loss (income) from equity affiliates	15,100,000	(13,200,000)
Provision for North Goonyella equipment loss	0	24,700,000
Foreign currency option contracts	(1,300,000)	2,400,000
Changes in current assets and liabilities:
Accounts receivable	138,100,000	20,800,000
Inventories	29,900,000	(42,500,000)
Other current assets	(13,300,000)	(32,000,000.0)
Accounts payable and accrued expenses	(133,900,000)	(52,700,000)
Asset retirement obligations	6,900,000	9,300,000
Workers’ compensation obligations	(500,000)	900,000
Postretirement benefit obligations	(14,800,000)	(31,200,000)
Pension obligations	200,000	(17,900,000)
Other, net	(2,600,000)	(14,800,000)
Net cash (used in) provided by continuing operations	(32,700,000)	398,600,000
Net cash used in discontinued operations	(20,400,000)	(21,600,000)
Net cash (used in) provided by operating activities	(53,100,000)	377,000,000.0
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development	(85,800,000)	(96,800,000)
Changes in accrued expenses related to capital expenditures	(14,300,000)	200,000
Proceeds from Insurance Settlement, Investing Activities	0	23,200,000
Proceeds from disposal of assets, net of receivables	12,000,000.0	15,800,000
Amount attributable to acquisition of Shoal Creek Mine	0	(2,400,000)
Contributions to joint ventures	(192,000,000.0)	(219,600,000)
Distributions from joint ventures	188,200,000	205,500,000
Advances to related parties	(23,100,000)	(4,500,000)
Cash receipts from Middlemount Coal Pty Ltd	0	14,700,000
Other, net	(600,000)	(100,000)
Net cash used in investing activities	(115,600,000)	(64,000,000.0)
Cash Flows From Financing Activities
Proceeds from (Repayments of) Other Long-term Debt	300,000,000.0	0
Repayments of long-term debt	(9,900,000)	(17,500,000)
Payments of Debt Issuance Costs	0	(800,000)
Common stock repurchases	0	(156,000,000.0)
Repurchase of employee common stock relinquished for tax withholding	(1,600,000)	(12,300,000)
Dividends paid	0	(229,300,000)
Distributions to noncontrolling interests	(3,500,000)	(14,400,000)
Net cash used in financing activities	285,000,000.0	(430,300,000)
Net change in cash, cash equivalents and restricted cash	116,300,000	(117,300,000)
Cash, cash equivalents and restricted cash at beginning of period	732,200,000	1,017,400,000
Cash, cash equivalents and restricted cash at end of period	$ 848,500,000	$ 900,100,000