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
Mar. 31, 2014
Dec. 31, 2013
Loss Contingencies [Line Items]    
Environmental $ 11.0 $ 8.4
Mine Reclamation and Closing Liability, current and noncurrent 295.3 312.6
Total environmental and mine closure obligations 306.3 321.0
Less current portion 5.6 11.3
Long term environmental and mine closure obligations 300.7 309.7
U.S. Iron Ore [Member] | Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent 136.4 152.2
Eastern Canadian Iron Ore [Member] | Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent 74.6 78.2
Asia Pacific Iron Ore [Member] | Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent 26.9 25.5
North American Coal [Member] | Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent 35.2 34.7
LTV Steel Mining Company [Member] | Previously Owned Or Operating Facilities [Member]
    
Loss Contingencies [Line Items]    
Mine Reclamation and Closing Liability, current and noncurrent $ 22.2 $ 22.0