CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows From Operating Activities
Net (loss) income	$ (1,873.8)	$ (185.1)	$ 663.8
Loss (income) from discontinued operations, net of income taxes	14.0	(3.2)	(18.1)
(Loss) income from continuing operations, net of income taxes	(1,859.8)	(188.3)	645.7
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	346.0	601.0	679.0
Noncash interest expense including loss on early extinguishment of debt	16.2	16.2	19.2
Noncash coal inventory revaluation	(0.7)	8.3	0.0
Deferred income taxes	27.8	39.4	35.5
Noncash share-based compensation	13.5	38.3	34.9
Asset impairment	1,487.4	270.2	0.0
Net gain on disposals	(15.2)	(2.1)	(48.2)
Loss (income) from equity affiliates	60.1	(3.4)	(68.1)
Provision for North Goonyella equipment loss	0.0	83.2	66.4
Gain on formation of United Wambo Joint Venture	0.0	(48.1)	0.0
Foreign currency option contracts	(13.0)	5.2	9.1
Noncash reorganization items, net	0.0	0.0	(12.8)
Changes in current assets and liabilities:
Accounts receivable	84.6	82.9	171.8
Inventories	70.6	(61.6)	50.2
Other current assets	21.0	(35.6)	(30.6)
Accounts payable and accrued expenses	(192.4)	(118.2)	(160.2)
Collateral arrangements	(15.0)	0.0	323.1
Asset retirement obligations	22.5	6.6	5.7
Workers’ compensation obligations	1.8	5.0	(1.8)
Postretirement benefit obligations	(12.1)	36.8	(151.1)
Pension obligations	(28.4)	(32.5)	(66.9)
Other, net	0.1	2.1	16.0
Net cash provided by continuing operations	15.0	705.4	1,516.9
Net cash used in discontinued operations	(24.7)	(28.0)	(27.2)
Net cash (used in) provided by operating activities	(9.7)	677.4	1,489.7
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development	(191.4)	(285.4)	(301.0)
Changes in accrued expenses related to capital expenditures	(6.1)	0.1	0.1
Federal coal lease expenditures	0.0	0.0	(0.5)
Insurance proceeds attributable to North Goonyella equipment losses	0.0	23.2	0.0
Proceeds from disposal of assets, net of receivables	27.1	30.0	76.4
Amount attributable to acquisition of Shoal Creek Mine	0.0	(2.4)	(387.4)
Contributions to joint ventures	(343.0)	(419.1)	(475.3)
Distributions from joint ventures	330.3	408.8	483.7
Advances to related parties	(23.2)	(27.3)	(13.8)
Cash receipts from Middlemount Coal Pty Ltd	0.0	14.7	106.7
Investment in equity securities	0.0	(3.0)	(10.0)
Other, net	(0.4)	(0.9)	3.8
Net cash used in investing activities	(206.7)	(261.3)	(517.3)
Cash Flows From Financing Activities
Proceeds from long-term debt	375.0	0.0	0.0
Repayments of long-term debt	(169.5)	(71.1)	(85.0)
Payment of debt issuance and other deferred financing costs	(7.0)	(6.4)	(21.2)
Common stock repurchases	0.0	(329.9)	(834.7)
Repurchase of employee common stock relinquished for tax withholding	(1.6)	(12.3)	(14.5)
Dividends paid	0.0	(258.1)	(59.6)
Distributions to noncontrolling interests	(3.5)	(23.5)	(10.3)
Other, net	0.0	0.0	0.1
Net cash provided by (used in) financing activities	193.4	(701.3)	(1,025.2)
Net change in cash, cash equivalents and restricted cash	(23.0)	(285.2)	(52.8)
Cash, cash equivalents and restricted cash at beginning of period	732.2	1,017.4	1,070.2
Cash, cash equivalents and restricted cash at end of period	$ 709.2	$ 732.2	$ 1,017.4