Quarterly report pursuant to Section 13 or 15(d)

Basis Of Presentation And Significant Accounting Policies (Investments In Unconsolidated Venture) (Details)

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Basis Of Presentation And Significant Accounting Policies (Investments In Unconsolidated Venture) (Details) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2011
Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]    
Investment $ 511.3 $ 509.0
Other Liabilities [Member] | Cockatoo [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 50.00% [1]  
Investment (4.5) [1] 10.5 [1]
Amapa [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 30.00%  
Investment 489.0 461.3
Investments In Ventures [Member] | AusQuest [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 30.00%  
Investment 5.7 24.1
Investments In Ventures [Member] | Hibbing [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 23.00% [2]  
Investment 2.1 [2] (5.8) [2]
Investments In Ventures [Member] | Other Equity Investees [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment $ 19.0 $ 18.9
[1] Recorded as Investments in ventures at December 31, 2010.
[2] Recorded as Other liabilities at December 31, 2010.