SEGMENT REPORTING (Summary of Assets by Segment) (Details) - USD ($) $ in Millions |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|---|
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý |
| Assets | $ 2,953.4 | $ 1,923.9 | $ 2,135.5 |
| U.S. Iron Ore [Member] | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý |
| Assets | 1,500.6 | 1,372.5 | 1,476.4 |
| Asia Pacific Iron Ore [Member] | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý |
| Assets | 138.8 | 155.1 | 202.5 |
| Total Segment Assets [Member] | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý |
| Assets | 1,639.4 | 1,527.6 | 1,678.9 |
| Corporate [Member] | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý |
| Assets | 1,314.0 | 396.3 | 441.7 |
| Discontinued Operations [Member] | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý |
| Disposal Group, Including Discontinued Operation, Assets | $ 0.0 | $ 0.0 | $ 14.9 |
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- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount classified as assets attributable to disposal group held for sale or disposed of. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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