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Property, Plant, Equipment and Mine Development | 3 Months Ended
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Mar. 31, 2022
Property, Plant and Equipment [Abstract] |
Property, Plant, Equipment and Mine Development | Property, Plant, Equipment and Mine Development The composition of property, plant, equipment and mine development, net, as of March 31, 2022 and December 31, 2021 is set forth in the table below:
| March 31, 2022 |  | December 31, 2021
| (Dollars in millions)
Land and coal interests | $ | 2,494.1 |  |  | $ | 2,494.1 |
Buildings and improvements | 590.2 |  |  | 550.8 |
Machinery and equipment | 1,370.9 |  |  | 1,386.2 |
Less: Accumulated depreciation, depletion and amortization | (1,551.9) |  |  | (1,480.5) |
Property, plant, equipment and mine development, net | $ | 2,903.3 |  |  | $ | 2,950.6 |
Asset Impairment and Other At-Risk Assets The Company has identified certain assets with an aggregate carrying value of approximately $0.5 billion at March 31, 2022 in its Other U.S. Thermal Mining and Corporate and Other segments whose recoverability is most sensitive to customer demand, customer concentration risk and future economic viability. The Company conducted a review of those assets as of March 31, 2022 and determined that no impairment charges were necessary as of that date.

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- Definition The entire disclosure for long-lived, physical asset used in normal conduct of business and not intended for resale. Includes, but is not limited to, work of art, historical treasure, and similar asset classified as collections. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 958 -SubTopic 360 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=120429125&loc=d3e99893-112916 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -URI http://asc.fasb.org/topic&trid=2155823 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 958 -SubTopic 360 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=120429125&loc=SL120174063-112916 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 958 -SubTopic 360 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=120429125&loc=d3e99779-112916 + Details
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