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PROPERTY, PLANT AND EQUIPMENT (Tables) | 12 Months Ended
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Dec. 31, 2015
Property, Plant and Equipment [Abstract] |
Value Of Each Of The Major Classes Of Consolidated Depreciable Assets | The following table indicates the value of each of the major classes of our consolidated depreciable assets as of December 31, 2015 and 2014:
| (In Millions)
| December 31,
| 2015 |  | 2014
Land rights and mineral rights | $ | 500.5 |  |  | $ | 500.5 |
Office and information technology | 71.0 |  |  | 73.7 |
Buildings | 60.4 |  |  | 59.8 |
Mining equipment | 594.0 |  |  | 585.1 |
Processing equipment | 516.8 |  |  | 510.2 |
Electric power facilities | 46.4 |  |  | 46.8 |
Land improvements | 24.8 |  |  | 24.7 |
Asset retirement obligation | 87.9 |  |  | 26.5 |
Other | 28.2 |  |  | 28.5 |
Construction in-progress | 40.3 |  |  | 14.4 |
| 1,970.3 |  |  | 1,870.2 |
Allowance for depreciation and depletion | (911.3 | ) |  | (799.7 | )
| $ | 1,059.0 |  |  | $ | 1,070.5 |
Book Value of Land and Mineral Rights Disclosure [Table Text Block] | The net book value of the land rights and mineral rights as of December 31, 2015 and 2014 is as follows:
| (In Millions)
| December 31,
| 2015 |  | 2014
Land rights | $ | 11.6 |  |  | $ | 11.6 |
Mineral rights: |  |  |
Cost | $ | 488.9 |  |  | $ | 488.9 |
Depletion | (108.4 | ) |  | (101.0 | )
Net mineral rights | $ | 380.5 |  |  | $ | 387.9 |

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- Definition Tabular disclosure of physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, balances by class of assets, depreciation and depletion expense and method used, including composite depreciation, and accumulated deprecation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.13) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 13 -Subparagraph b -Article 5 + Details
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