Annual report pursuant to Section 13 and 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details)

v2.4.0.6
FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2011
Jun. 30, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2012
Empire [Member]
Dec. 31, 2011
Empire [Member]
Dec. 31, 2002
Empire [Member]
Dec. 31, 2002
Prior [Member]
Empire [Member]
Dec. 31, 2002
Current [Member]
Empire [Member]
Dec. 31, 2012
Other Current Assets [Member]
Empire [Member]
Dec. 31, 2011
Other Current Assets [Member]
Empire [Member]
Dec. 31, 2012
U.S. Iron Ore [Member]
Dec. 31, 2011
U.S. Iron Ore [Member]
Dec. 31, 2012
Amapa [Member]
Dec. 31, 2012
Wabush [Member]
Dec. 31, 2012
Wabush [Member]
Fair Value, Assets And Liabilities Components [Line Items]                                
Transfer of derivative assets from level 3 to level 2   $ 20.0 $ 0 $ 20.0                        
Transfer of derivative assets from level 2 to level 3 49.0   0 49.0                        
Management Estimate of 62% Fe     62.00%                          
Maximum deferred portion of supplemental payments                       22.3        
Supply agreement, customer receivable, stated interest rate     9.00%                          
Supply agreement, customer receivable, description of variable rate basis     prime rate                          
Other current assets 166.3   216.2 166.3                 22.3      
Supply agreement, customer receivable, basis spread on variable rate     3.50%                          
Other non-current assets 191.2   193.6 191.2                 22.3      
Fair value of the receivable         21.3 30.7           21.3 20.8      
Estimated credit-adjusted risk-free interest rate         2.85% 2.58%           2.81% 4.50%      
Interest Percentage               46.70%                
Equity Method Investments, Fair Value Disclosure                           72.5    
Percent ownership interest after transaction                 79.00%              
Long term accounts notes and loans receivable net noncurrent         19.3 26.5 120.0     10.0 10.0          
Goodwill impairment     1,000.0 27.8                     2.7 2.7
Impairment of long-lived assets                               $ 49.9