Annual report pursuant to Section 13 and 15(d)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)

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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Northshore [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province Minnesota  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%  
Segment Reporting Information, Description of Products and Services Iron Ore  
United Taconite [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province Minnesota  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%  
Segment Reporting Information, Description of Products and Services Iron Ore  
Wabush [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province Newfoundland and Labrador/ Quebec, Canada  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%  
Segment Reporting Information, Description of Products and Services Iron Ore  
Bloom Lake [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province Quebec, Canada  
Noncontrolling Interest, Ownership Percentage by Parent 82.80% 75.00%
Segment Reporting Information, Description of Products and Services Iron Ore  
Tilden [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province Michigan  
Noncontrolling Interest, Ownership Percentage by Parent 85.00%  
Segment Reporting Information, Description of Products and Services Iron Ore  
Empire [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province Michigan  
Noncontrolling Interest, Ownership Percentage by Parent 79.00%  
Segment Reporting Information, Description of Products and Services Iron Ore  
Koolyanobbing [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province Western Australia  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%  
Segment Reporting Information, Description of Products and Services Iron Ore  
Pinnacle [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province West Virginia  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%  
Segment Reporting Information, Description of Products and Services Coal  
Oak Grove [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province Alabama  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%  
Segment Reporting Information, Description of Products and Services Coal  
CLCC [Member]
   
Related Party Transaction [Line Items]    
Entity Address, State or Province West Virginia  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%  
Segment Reporting Information, Description of Products and Services Coal