Quarterly report pursuant to Section 13 or 15(d)

Fair Value Of Financial Instruments (Narrative) (Details)

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Fair Value Of Financial Instruments (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Dec. 31, 2011
Dec. 31, 2002
Fair Value, Assets And Liabilities Components [Line Items]      
Interest rate on long term receivable the higher of 9 percent or the prime rate plus 350 basis points    
Other non-current assets $ 186.8 $ 191.2  
U.S. Iron Ore [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Maximum deferred portion of supplemental payments 22.3    
Other non-current assets 22.3    
Fair value of the receivable 21.2 20.8  
Estimated credit-adjusted risk-free interest rate 3.30%    
Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Long term accounts notes and loans receivable net noncurrent 24.8 26.5 120.0
Fair value of the receivable $ 28.6 $ 30.7  
Estimated credit-adjusted risk-free interest rate 2.02%    
Current [Member] | Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Percent ownership interest     79.00%
Prior [Member] | Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Percent ownership interest     46.70%