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Basis Of Presentation And Significant Accounting Policies (Investments In Unconsolidated Ventures) (Detail) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]    
Investment $ 508.7 $ 504.8
Amapa [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment 493.4 498.6
Interest Percentage 30.00%  
Cockatoo [Member] | Other Liabilities [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment (16.7) (15.0)
Interest Percentage 50.00%  
Hibbing [Member] | Other Liabilities [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment (5.8) (6.8)
Interest Percentage 23.00%  
Other Equity Investees [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment $ 37.8 $ 28.0