Quarterly report pursuant to Section 13 or 15(d)

ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details)

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ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Loss Contingencies [Line Items]    
Environmental $ 8.4 $ 15.7
Mine Reclamation and Closing Liability, current and noncurrent 301.8 249.4
Total environmental and mine closure obligations 310.2 265.1
Less current portion 10.7 12.3
Long term environmental and mine closure obligations 299.5 252.8
U.S. Iron Ore [Member] | Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent 139.6 81.2
Eastern Canadian Iron Ore [Member] | Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent 76.6 88.9
Asia Pacific Iron Ore [Member] | Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent 26.2 22.4
North American Coal [Member] | Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent 40.0 38.6
LTV Steel Mining Company [Member] | Previously Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent $ 19.4 $ 18.3