Quarterly report pursuant to Section 13 or 15(d)

Basis Of Presentation And Significant Accounting Policies (Investments In Unconsolidated Ventures) (Detail)

v2.4.0.6
Basis Of Presentation And Significant Accounting Policies (Investments In Unconsolidated Ventures) (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]    
Investment $ 488.3 $ 504.8
Amapa [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Percent ownership interest 30.00%  
Investment 479.2 498.6
Cockatoo [Member] | Other Liabilities [Member]
   
Schedule of Equity Method Investments [Line Items]    
Percent ownership interest 50.00%  
Investment (28.7) (15.0)
Hibbing [Member] | Other Liabilities [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment 0.8 (6.8)
Other Equity Investees [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment $ 37.0 $ 28.0