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ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 USD ($) T | Mar. 31, 2017 USD ($)
Accrual for Environmental Loss Contingencies, Period Increase (Decrease) | $ 9.2 |
Reserve increase (decrease), tons | T | 115,000,000 |
Selenium [Domain] |  |
Accrual for Environmental Loss Contingencies, Period Increase (Decrease) | $ (29.6) |
Eastern Canadian Iron Ore [Member] | Owned Or Operating Facilities [Member] |  |
Mine Reclamation and Closing Liability, current and noncurrent | $ 206.8 | $ 211.0

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- Definition Increase (decrease) in the accrual for environmental loss contingencies during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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