Annual report pursuant to Section 13 and 15(d)

GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Narrative) (Details)

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GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Goodwill [Line Items]      
Goodwill, Impairment Loss $ 80.9 $ 1,000.0  
Product 5,346.6 5,520.9 6,321.3
Below-market sales contracts, remaining contract life 3 years    
Assets, Fair Value Disclosure, Nonrecurring 47.9 72.5  
Impairment Charges 318.4 1,415.3  
Cost of Sales [Member]
     
Goodwill [Line Items]      
Amortization expense relating to intangible assets 19.9 22.5 17.7
Product Revenues [Member] | Sales Revenue, Goods, Net [Member]
     
Goodwill [Line Items]      
Product 45.9 46.3 57.0
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
     
Goodwill [Line Items]      
Goodwill, Impairment Loss 80.9    
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
     
Goodwill [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure 46.3    
Impairment of Long-Lived Assets Held-for-use 155.4    
CQIM Reporting Unit [Member]
     
Goodwill [Line Items]      
Goodwill, Fair Value Disclosure 0 0  
Goodwill, Impairment Loss   997.3  
Wabush [Member]
     
Goodwill [Line Items]      
Goodwill, Fair Value Disclosure   0  
Impairment of Intangible Assets, Finite-lived 9.5    
Goodwill, Impairment Loss   2.7  
Property, Plant, and Equipment, Fair Value Disclosure   0  
Impairment of Long-Lived Assets Held-for-use 140.1 49.9  
Finite-lived Intangible Assets, Fair Value Disclosure 1.6    
Other Asset Impairment Charges 14.5    
Fair Value, Inputs, Level 1 [Member]
     
Goodwill [Line Items]      
Assets, Fair Value Disclosure, Nonrecurring 0 0  
Fair Value, Inputs, Level 1 [Member] | Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
     
Goodwill [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure 0    
Fair Value, Inputs, Level 1 [Member] | CQIM Reporting Unit [Member]
     
Goodwill [Line Items]      
Goodwill, Fair Value Disclosure 0 0  
Fair Value, Inputs, Level 1 [Member] | Wabush [Member]
     
Goodwill [Line Items]      
Goodwill, Fair Value Disclosure   0  
Property, Plant, and Equipment, Fair Value Disclosure   0  
Finite-lived Intangible Assets, Fair Value Disclosure 0    
Fair Value, Inputs, Level 2 [Member]
     
Goodwill [Line Items]      
Assets, Fair Value Disclosure, Nonrecurring 0 0  
Fair Value, Inputs, Level 2 [Member] | Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
     
Goodwill [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure 0    
Fair Value, Inputs, Level 2 [Member] | CQIM Reporting Unit [Member]
     
Goodwill [Line Items]      
Goodwill, Fair Value Disclosure 0 0  
Fair Value, Inputs, Level 2 [Member] | Wabush [Member]
     
Goodwill [Line Items]      
Goodwill, Fair Value Disclosure   0  
Property, Plant, and Equipment, Fair Value Disclosure   0  
Finite-lived Intangible Assets, Fair Value Disclosure 0    
Fair Value, Inputs, Level 3 [Member]
     
Goodwill [Line Items]      
Assets, Fair Value Disclosure, Nonrecurring 47.9 72.5  
Fair Value, Inputs, Level 3 [Member] | Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]
     
Goodwill [Line Items]      
Property, Plant, and Equipment, Fair Value Disclosure 46.3    
Fair Value, Inputs, Level 3 [Member] | CQIM Reporting Unit [Member]
     
Goodwill [Line Items]      
Goodwill, Fair Value Disclosure 0 0  
Fair Value, Inputs, Level 3 [Member] | Wabush [Member]
     
Goodwill [Line Items]      
Goodwill, Fair Value Disclosure   0  
Property, Plant, and Equipment, Fair Value Disclosure   0  
Finite-lived Intangible Assets, Fair Value Disclosure 1.6    
Amapa [Member]
     
Goodwill [Line Items]      
Equity Method Investments, Fair Value Disclosure 0 72.5  
Equity Method Investment, Other than Temporary Impairment 67.6 365.4  
Amapa [Member] | Fair Value, Inputs, Level 1 [Member]
     
Goodwill [Line Items]      
Equity Method Investments, Fair Value Disclosure 0 0  
Amapa [Member] | Fair Value, Inputs, Level 2 [Member]
     
Goodwill [Line Items]      
Equity Method Investments, Fair Value Disclosure 0 0  
Amapa [Member] | Fair Value, Inputs, Level 3 [Member]
     
Goodwill [Line Items]      
Equity Method Investments, Fair Value Disclosure $ 0 $ 72.5