ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2017 |
Sep. 30, 2018 |
|
| Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent | $ 171.3 | $ 177.3 |
| U.S. Iron Ore [Member] | ||
| Accrual for Environmental Loss Contingencies, Period Increase (Decrease) | $ (26.2) |
| X | ||||||||||
- Definition Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent No definition available.
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| X | ||||||||||
- Definition Increase (decrease) in the accrual for environmental loss contingencies during the reporting period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Details
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