Quarterly report pursuant to Section 13 or 15(d)

Environmental And Mine Closure Obligations (Summary Of Mine Closure Obligations) (Detail)

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Environmental And Mine Closure Obligations (Summary Of Mine Closure Obligations) (Detail) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Loss Contingencies [Line Items]    
Environmental $ 14.5 $ 15.5
Total mine closure 229.6 220.2
Total environmental and mine closure obligations 244.1 235.7
Less current portion 12.7 13.7
Long term environmental and mine closure obligations 231.4 222.0
Previously Owned Or Operating Facilities [Member] | LTV Steel Mining Company [Member]
   
Loss Contingencies [Line Items]    
Total mine closure 16.9 16.5
Owned Or Operating Facilities [Member] | U.S. Iron Ore [Member]
   
Loss Contingencies [Line Items]    
Total mine closure 77.9 74.3
Owned Or Operating Facilities [Member] | Eastern Canadian Iron Ore [Member]
   
Loss Contingencies [Line Items]    
Total mine closure 71.5 68.0
Owned Or Operating Facilities [Member] | North American Coal [Member]
   
Loss Contingencies [Line Items]    
Total mine closure 37.5 36.3
Owned Or Operating Facilities [Member] | Asia Pacific Iron Ore [Member]
   
Loss Contingencies [Line Items]    
Total mine closure 16.8 16.3
Owned Or Operating Facilities [Member] | Other Regions [Member]
   
Loss Contingencies [Line Items]    
Total mine closure $ 9.0 $ 8.8