| ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014 | 
|---|---|---|
| Environmental Remediation Obligations [Abstract] | ||
| Total environmental and mine closure obligations | $ 169.0clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrentAndNoncurrent | $ 170.8clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrentAndNoncurrent | 
| X | ||||||||||
| 
- Definition Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent No definition available. 
 | 
| X | ||||||||||
| 
- Details 
 |