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, 2013
Dec. 31, 2012
Loss Contingencies [Line Items]    
Environmental $ 15.4 $ 15.7
Mine Reclamation and Closing Liability, current and noncurrent 237.0 249.4
Total environmental and mine closure obligations 252.4 265.1
Less current portion 12.0 12.3
Long term environmental and mine closure obligations 240.4 252.8
Previously Owned Or Operating Facilities [Member] | LTV Steel Mining Company [Member]
   
Loss Contingencies [Line Items]    
Mine closure 18.7 18.3
Owned Or Operating Facilities [Member] | U.S. Iron Ore [Member]
   
Loss Contingencies [Line Items]    
Mine closure 83.1 81.2
Owned Or Operating Facilities [Member] | Eastern Canadian Iron Ore [Member]
   
Loss Contingencies [Line Items]    
Mine closure 73.4 88.9
Owned Or Operating Facilities [Member] | Asia Pacific Iron Ore [Member]
   
Loss Contingencies [Line Items]    
Mine closure 22.7 22.4
Owned Or Operating Facilities [Member] | North American Coal [Member]
   
Loss Contingencies [Line Items]    
Mine closure $ 39.1 $ 38.6