Annual report pursuant to Section 13 and 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details)

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FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2002
Fair Value, Assets And Liabilities Components [Line Items]      
Management Estimate of 62% Fe 62.00%    
Supply agreement, customer receivable, basis spread on variable rate 3.50%    
Goodwill, Impairment Loss $ 80.9 $ 1,000.0  
Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Loans Receivable, Fair Value Disclosure 11.9 21.3  
Fair Value Assumptions, Risk Free Interest Rate 1.28% 2.85%  
Accounts, Notes, Loans and Financing Receivable, Net, Noncurrent 11.3 19.3 120.0
Prior [Member] | Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Interest Percentage     46.70%
Current [Member] | Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Percent ownership interest after transaction     79.00%
Other Current Assets [Member] | Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Other current assets   10.0  
Customer Supplemental Payments [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Maximum deferred portion of supplemental payments 22.3    
Supply agreement, customer receivable, stated interest rate 9.00%    
Supply agreement, customer receivable, description of variable rate basis prime rate    
Payments for (Proceeds from) Loans Receivable 22.3    
Loans Receivable, Fair Value Disclosure   21.3  
Fair Value Assumptions, Risk Free Interest Rate   2.81%  
Customer Supplemental Payments [Member] | Other Current Assets [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Other current assets   22.3  
Amapa [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Equity Method Investments, Fair Value Disclosure 0 72.5  
Equity Method Investment, Other than Temporary Impairment 67.6 365.4  
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Goodwill, Impairment Loss 80.9    
CQIM Reporting Unit [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Goodwill, Impairment Loss   997.3  
Wabush [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Goodwill, Impairment Loss   2.7  
Other Asset Impairment Charges 14.5    
Impairment of Long-Lived Assets Held-for-use $ 140.1 $ 49.9