CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash Flows From Operating Activities
Net income (loss)	$ 371.4	$ (1,873.8)	$ (185.1)
(Income) loss from discontinued operations, net of income taxes	(24.0)	14.0	(3.2)
Income (loss) from continuing operations, net of income taxes	347.4	(1,859.8)	(188.3)
Adjustments to reconcile income (loss) from continuing operations, net of income taxes to net cash provided by (used in) operating activities:
Depreciation, depletion and amortization	308.7	346.0	601.0
Noncash interest expense, net	21.3	16.2	16.0
Deferred income taxes	(7.5)	27.8	39.4
Noncash share-based compensation	10.0	13.5	38.3
Asset impairment	0.0	1,487.4	270.2
Net gain on disposals	(31.5)	(15.2)	(2.1)
Net (gain) loss on early debt extinguishment	(33.2)	0.0	0.2
(Income) loss from equity affiliates	(82.1)	60.1	(3.4)
Provision for North Goonyella equipment loss	0.0	0.0	83.2
Gain on formation of United Wambo Joint Venture	0.0	0.0	(48.1)
Foreign currency option contracts	5.8	(13.0)	5.2
Changes in current assets and liabilities:
Accounts receivable	(105.6)	84.6	82.9
Inventories	35.0	69.9	(53.3)
Other current assets	(57.6)	21.0	(35.6)
Accounts payable and accrued expenses	128.1	(192.4)	(118.2)
Collateral arrangements	(6.3)	(15.0)	0.0
Asset retirement obligations	6.8	22.5	6.6
Workers’ compensation obligations	(2.0)	1.8	5.0
Postretirement benefit obligations	(108.2)	(12.1)	36.8
Pension obligations	11.6	(28.4)	(32.5)
Other, net	0.0	0.1	2.1
Net cash provided by continuing operations	440.7	15.0	705.4
Net cash used in discontinued operations	(20.7)	(24.7)	(28.0)
Net cash provided by (used in) operating activities	420.0	(9.7)	677.4
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development	(183.1)	(191.4)	(285.4)
Changes in accrued expenses related to capital expenditures	7.4	(6.1)	0.1
Insurance proceeds attributable to North Goonyella equipment losses	0.0	0.0	23.2
Proceeds from disposal of assets, net of receivables	17.8	27.1	30.0
Amount attributable to acquisition of Shoal Creek Mine	0.0	0.0	(2.4)
Contributions to joint ventures	(485.6)	(343.0)	(419.1)
Distributions from joint ventures	470.8	330.3	408.8
Advances to related parties	(0.5)	(23.2)	(27.3)
Cash receipts from Middlemount Coal Pty Ltd and other related parties	44.7	0.0	14.7
Investment in equity securities	0.0	0.0	(3.0)
Other, net	(3.0)	(0.4)	(0.9)
Net cash used in investing activities	(131.5)	(206.7)	(261.3)
Cash Flows From Financing Activities
Proceeds from long-term debt	0.0	375.0	0.0
Repayments of long-term debt	(285.3)	(169.5)	(71.1)
Payment of debt issuance and other deferred financing costs	(22.5)	(7.0)	(6.4)
Proceeds from common stock issuances, net of costs	269.8	0.0	0.0
Common stock repurchases	0.0	0.0	(329.9)
Repurchase of employee common stock relinquished for tax withholding	(1.4)	(1.6)	(12.3)
Dividends paid	0.0	0.0	(258.1)
Distributions to noncontrolling interests	(4.0)	(3.5)	(23.5)
Net cash (used in) provided by financing activities	(43.4)	193.4	(701.3)
Net change in cash, cash equivalents and restricted cash	245.1	(23.0)	(285.2)
Cash, cash equivalents and restricted cash at beginning of period	709.2	732.2	1,017.4
Cash, cash equivalents and restricted cash at end of period	$ 954.3	$ 709.2	$ 732.2