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ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Narrative) (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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Environmental Remediation Obligations [Abstract] |  |
Total environmental and mine closure obligations | $ 169.0 clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrentAndNoncurrent | $ 170.8 clf_EnvironmentalLossContingencyAndMineReclamationAndClosingLiabilityCurrentAndNoncurrent

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- Definition Environmental Loss Contingency And Mine Reclamation And Closing Liability Current And Noncurrent + References No definition available. + Details
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Namespace Prefix: | clf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration