Impairment to Unallocated Coal Reserves

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- Definition

Planned Divestiture, Agreed Upon Proceeds from Divestiture

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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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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Long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Asset Impairment Textuals (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended	12 Months Ended
Asset Impairment Textuals (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Apr. 01, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Nov. 30, 2016
Impaired Long-Lived Assets Held and Used [Line Items]
Carrying Value of Australian Metallurgical Assets	$ 4,679.1			$ 5,111.9	$ 4,679.1	$ 5,207.0
Asset impairment charges	250.2	$ 20.0	$ 30.5	0.0	270.2	0.0
Equity method investment			0.0	0.0	9.0	0.0
Western U.S. Mining
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges					172.0
Midwestern U.S. Mining
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges					20.0
Corporate and Other
Impaired Long-Lived Assets Held and Used [Line Items]
Carrying Value of Australian Metallurgical Assets	291.3			$ 249.2	291.3	$ 365.3
Impairment to Unallocated Coal Reserves					69.2
Midwestern U.S. Mining and Corporate and Other [Domain]
Impaired Long-Lived Assets Held and Used [Line Items]
Long-Lived Assets	$ 89.0				$ 89.0
Metropolitan Collieries Pty Ltd
Impaired Long-Lived Assets Held and Used [Line Items]
Planned Divestiture, Agreed Upon Proceeds from Divestiture							$ 200.0
Contract Termination \| Midwestern U.S. Mining
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment charges			$ 30.5