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PROPERTY: | 12 Months Ended
--- | ---
Dec. 31, 2020
PROPERTY: |
PROPERTY: | NOTE 5—PROPERTY: ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | At December 31,
(in millions) |  | 2020 |  | 2019
Buildings and equipment | ​ | $ | 15,561.9 | ​ | $ | 15,016.1
Construction in progress | ​ |  | 1,481.6 | ​ |  | 1,294.8
Mine development | ​ |  | 272.8 | ​ |  | 267.5
Mineral assets | ​ | ​ | 83.2 | ​ | ​ | 83.2
Land, other than mineral | ​ |  | 235.8 | ​ |  | 200.1
Total property | ​ |  | 17,635.3 | ​ |  | 16,861.7
Accumulated depreciation, amortization and depletion | ​ |  | (8,176.6) | ​ |  | (7,490.7)
Total property and mine development, net | ​ | $ | 9,458.7 | ​ | $ | 9,371.0
​ Depreciation and depletion expense for the years ended December 31, 2020, 2019 and 2018, amounted to $766.4 million, $759.9 million and $668.9 million, respectively.

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