Amount contributed to the Combined Benefit Fund

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Amount represents the upper future estimate of the Company's annual cash costs related to the Combined Benefit Fund.

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Combined Benefit Fund Liability

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estimated fund obligations

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Number of Buyers

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Number of Retirees

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Potential exposure from Patriot bankruptcy related to certain federal and state black lung occupational disease liabilities

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Amount after tax of income (loss) from a discontinued operation including the portion attributable to the noncontrolling interest. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Aggregate carrying amount of the estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs.

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Amount awarded to other party in judgment or settlement of litigation.

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Amount of loss contingency liability.

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Discontinued Operations - Patriot Related Matters (Details) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 25, 2017 USD ($)	Sep. 30, 2020 USD ($) retiree	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) retiree	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Oct. 09, 2015 buyer	Dec. 31, 2007 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of retirees \| retiree		0		0
Estimated fund obligation		$ 40.0		$ 40.0
Loss from discontinued operations, net of income taxes		2.3	$ 3.8	6.8	$ 10.6
Amount contributed to the combined benefit fund		0.4	0.4	1.2	1.4
Combined benefit fund liability		14.4		14.4		$ 15.2
Minimum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Combined benefit fund future estimate		1.0
Maximum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Combined benefit fund future estimate		2.0
Combined benefit fund
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss from discontinued operations, net of income taxes		0.1	$ 0.2	0.3	$ 0.5
Patriot
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of buyers \| buyer							2
Spinoff \| Patriot \| Black Lung Occupational Disease Liability
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Initially determined potential exposure from patriot bankruptcy								$ 150.0
Potential exposure from patriot bankruptcy		85.9		85.9		85.7
Spinoff \| UMWA 1974 Pension Plan (UMWA Plan) Litigation \| Patriot
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Settlement of claim, amount awarded to other party	$ 75.0
Litigation settlement, liability		$ 13.2		$ 13.2		$ 26.0