Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details)

v2.4.0.8
FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2014
Dec. 31, 2013
Fair Value, Assets And Liabilities Components [Line Items]    
Management Estimate of 62% Fe 62.00%  
Goodwill, Impairment Loss $ 0 $ 80.9
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
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
   
Fair Value, Assets And Liabilities Components [Line Items]    
Impairment of Long-Lived Assets Held-for-use   155.4
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
   
Fair Value, Assets And Liabilities Components [Line Items]    
Goodwill, Impairment Loss   $ 80.9