Annual report pursuant to Section 13 and 15(d)

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

v3.3.1.900
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Investments In Unconsolidated Ventures) (Details)
$ in Millions
12 Months Ended
Dec. 31, 2015
USD ($)
Facility
Dec. 31, 2014
USD ($)
Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]      
Investment $ (2.4) $ 4.1  
Asia Pacific Iron Ore [Member]      
Schedule of Equity Method Investments [Line Items]      
Number Of Mines | Facility 1    
Investments in Ventures [Member] | Amapa [Member]      
Schedule of Equity Method Investments [Line Items]      
Ownership interest, equity method investment     30.00%
Investments in Ventures [Member] | Hibbing [Member]      
Schedule of Equity Method Investments [Line Items]      
Ownership interest, equity method investment [1] 23.00%    
Other Noncurrent Liabilities [Member] | Hibbing [Member]      
Schedule of Equity Method Investments [Line Items]      
Investment $ (2.4)    
Other Noncurrent Assets [Member] | Hibbing [Member]      
Schedule of Equity Method Investments [Line Items]      
Investment   3.1  
Other Noncurrent Assets [Member] | Other Equity Investees [Member]      
Schedule of Equity Method Investments [Line Items]      
Investment $ 0.0 [2] $ 1.0  
[1] At December 31, 2014, the classification for Hibbing was Other non-current assets.
[2] At December 31, 2015, no Other equity method investments remain.