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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)
3 Months Ended
Mar. 31, 2013
Northshore [Member]
 
Related Party Transaction [Line Items]  
Location Minnesota
Ownership Interest 100.00%
Operation Iron Ore
United Taconite [Member]
 
Related Party Transaction [Line Items]  
Location Minnesota
Ownership Interest 100.00%
Operation Iron Ore
Wabush [Member]
 
Related Party Transaction [Line Items]  
Location Newfoundland and Labrador/Quebec, Canada
Ownership Interest 100.00%
Operation Iron Ore
Bloom Lake [Member]
 
Related Party Transaction [Line Items]  
Location Quebec, Canada
Ownership Interest 75.00%
Operation Iron Ore
Tilden [Member]
 
Related Party Transaction [Line Items]  
Location Michigan
Ownership Interest 85.00%
Operation Iron Ore
Empire [Member]
 
Related Party Transaction [Line Items]  
Location Michigan
Ownership Interest 79.00%
Operation Iron Ore
Koolyanobbing [Member]
 
Related Party Transaction [Line Items]  
Location Western Australia
Ownership Interest 100.00%
Operation Iron Ore
Pinnacle [Member]
 
Related Party Transaction [Line Items]  
Location West Virginia
Ownership Interest 100.00%
Operation Coal
Oak Grove [Member]
 
Related Party Transaction [Line Items]  
Location Alabama
Ownership Interest 100.00%
Operation Coal
CLCC [Member]
 
Related Party Transaction [Line Items]  
Location West Virginia
Ownership Interest 100.00%
Operation Coal