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Property, Plant, Equipment and Mine Development | 9 Months Ended
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Sep. 30, 2023
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 September 30, 2023 and December 31, 2022 is set forth in the table below:
| September 30, 2023 |  | December 31, 2022
| (Dollars in millions)
Land and coal interests | $ | 2,511.9 |  |  | $ | 2,514.7 |
Buildings and improvements | 633.5 |  |  | 594.2 |
Machinery and equipment | 1,671.0 |  |  | 1,543.1 |
Less: Accumulated depreciation, depletion and amortization | (2,010.9) |  |  | (1,787.0) |
Property, plant, equipment and mine development, net | $ | 2,805.5 |  |  | $ | 2,865.0 |
Asset Impairment and Other At-Risk Assets The Company identified certain assets with an aggregate carrying value of approximately $388 million at September 30, 2023 in its Powder River Basin and Other U.S. Thermal segments whose recoverability is most sensitive to customer demand and customer concentration risk. The Company conducted a review of those assets as of September 30, 2023 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://fasb.org/us-gaap/role/ref/legacyRef -Topic 360 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org//360/tableOfContent Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 6 -SubTopic 360 -Topic 958 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480321/958-360-50-6 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d) -SubTopic 360 -Topic 958 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480321/958-360-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 7 -SubTopic 360 -Topic 958 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480321/958-360-50-7 + Details
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