Quarterly report pursuant to Section 13 or 15(d)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Investments In Unconsolidated Ventures) (Details)

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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Investments In Unconsolidated Ventures) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]    
Investment $ 106.4 $ 108.4
Amapa [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 30.00%  
Total percentage of Amapa sold 100.00%  
Investment 96.9 101.9
Cockatoo [Member] | Other Liabilities [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 50.00%  
Investment (25.4) (25.3)
Hibbing [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment 1.4 [1]  
Hibbing [Member] | Other Liabilities [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment   (2.1) [1]
Other Equity Investees [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Investment $ 33.5 $ 33.9
Hibbing [Member] | Hibbing [Member] | Investments In Ventures [Member]
   
Schedule of Equity Method Investments [Line Items]    
Interest Percentage 23.00% [1]  
[1] At December 31, 2012 the classification for Hibbing was Other liabilities.