Annual report pursuant to Section 13 and 15(d)

Business Summary And Significant Accounting Policies (Investments In Unconsolidated Ventures) (Details)

v2.4.0.6
Business Summary And Significant Accounting Policies (Investments In Unconsolidated Ventures) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]    
Investment $ 504.8 $ 509.0
Amapa [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 30.00%  
Amapa [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 30.00%  
Investment 498.6 461.3
AusQuest [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 30.00%  
AusQuest [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 30.00%  
Investment 3.7 24.1
Cockatoo [Member] | Other Liabilities [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 50.00% [1]  
Investment (15.0) [1] 10.5 [1]
Hibbing [Member] | Other Liabilities [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 23.00%  
Investment (6.8) (5.8)
Other Equity Investees [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment $ 24.3 $ 18.9
[1] Recorded as Investments in ventures at December 31, 2010.