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PROPERTY, PLANT AND EQUIPMENT (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015 | Mar. 31, 2014
Property, Plant and Equipment [Line Items] |  |
Depreciation And Depletion | $ 28.7 clf_DepreciationAndDepletionExpense | $ 67.7 clf_DepreciationAndDepletionExpense

X
- Definition The aggregate expense recognized in the current period that allocates the cost of tangible assets or depleting assets to periods that benefit from use of the assets. + References No definition available. + Details
Name: | clf_DepreciationAndDepletionExpense
Namespace Prefix: | clf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration