CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash Flows From Operating Activities
Net income (loss)	$ 1,319.1	$ 371.4	$ (1,873.8)
(Income) loss from discontinued operations, net of income taxes	(1.7)	(24.0)	14.0
Income (loss) from continuing operations, net of income taxes	1,317.4	347.4	(1,859.8)
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	317.6	308.7	346.0
Noncash interest expense, net	17.7	21.3	16.2
Deferred income taxes	(81.6)	(7.5)	27.8
Noncash share-based compensation	8.4	10.0	13.5
Asset impairment	11.2	0.0	1,487.4
Net gain on disposals	(29.2)	(31.5)	(15.2)
Net loss (gain) on early debt extinguishment	57.9	(33.2)	0.0
(Income) loss from equity affiliates	(131.2)	(82.1)	60.1
Foreign currency option contracts	2.3	5.8	(13.0)
Changes in current assets and liabilities:
Accounts receivable	(115.0)	(105.6)	84.6
Inventories	(69.4)	35.0	69.9
Other current assets	(29.3)	(57.6)	21.0
Accounts payable and accrued expenses	68.0	128.1	(192.4)
Collateral arrangements	(53.3)	(6.3)	(15.0)
Asset retirement obligations	(22.3)	6.8	22.5
Workers’ compensation obligations	(0.9)	(2.0)	1.8
Postretirement benefit obligations	(109.3)	(108.2)	(12.1)
Pension obligations	18.6	11.6	(28.4)
Other, net	2.7	0.0	0.1
Net cash provided by continuing operations	1,180.3	440.7	15.0
Net cash used in discontinued operations	(6.7)	(20.7)	(24.7)
Net cash provided by (used in) operating activities	1,173.6	420.0	(9.7)
Cash Flows From Investing Activities
Additions to property, plant, equipment and mine development	(221.5)	(183.1)	(191.4)
Changes in accrued expenses related to capital expenditures	(2.7)	7.4	(6.1)
Proceeds from disposal of assets, net of receivables	40.6	17.8	27.1
Contributions to joint ventures	(645.9)	(485.6)	(343.0)
Distributions from joint ventures	631.6	470.8	330.3
Advances to related parties	(1.5)	(0.5)	(23.2)
Cash receipts from Middlemount Coal Pty Ltd and other related parties	171.8	44.7	0.0
Other, net	(1.1)	(3.0)	(0.4)
Net cash used in investing activities	(28.7)	(131.5)	(206.7)
Cash Flows From Financing Activities
Proceeds from long-term debt	545.0	0.0	375.0
Repayments of long-term debt	(1,407.4)	(285.3)	(169.5)
Payment of debt issuance and other deferred financing costs	(21.1)	(22.5)	(7.0)
Proceeds from common stock issuances, net of costs	222.0	269.8	0.0
Repurchase of employee common stock relinquished for tax withholding	(2.6)	(1.4)	(1.6)
Distributions to noncontrolling interests	(17.5)	(4.0)	(3.5)
Net cash (used in) provided by financing activities	(681.6)	(43.4)	193.4
Net change in cash, cash equivalents and restricted cash	463.3	245.1	(23.0)
Cash and cash equivalents	1,307.3	954.3
Restricted cash included in “Restricted cash and collateral arrangements”	110.3
Cash, cash equivalents and restricted cash at beginning of period	954.3	709.2	732.2
Cash, cash equivalents and restricted cash at end of period (1)	$ 1,417.6	$ 954.3	$ 709.2