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FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2014
Sep. 30, 2014
Dec. 31, 2013
Fair Value, Assets And Liabilities Components [Line Items]      
Management Estimate of 62% Fe   62.00%  
Goodwill, Impairment Loss   $ 73.5 $ 80.9
Tangible Asset Impairment Charges 7,674.3 7,699.6  
Amapa [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Equity Method Investments, Fair Value Disclosure     0
Equity Method Investment, Other than Temporary Impairment     67.6
Asia Pacific Iron Ore [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Goodwill, Impairment Loss   73.5  
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Tangible Asset Impairment Charges     155.4
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Goodwill, Impairment Loss     $ 80.9