Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Financial Instruments (Carrying Value and Fair Value of Financial Instruments Disclosure) (Details)

 v2.3.0.11
Fair Value of Financial Instruments (Carrying Value and Fair Value of Financial Instruments Disclosure) (Details) (USD $)
In Millions
Jun. 30, 2011
Dec. 31, 2010
Long-term debt:    
Total long-term debt $ 3,898.8 $ 1,713.1
Term Loan $1.25 Billion [Member] | Carrying Value [Member]
   
Long-term debt:    
Senior notes 1,187.5  
Term Loan $1.25 Billion [Member] | Fair Value [Member]
   
Long-term debt:    
Senior notes 1,187.5  
Senior Notes $1.3 Billion [Member] | Carrying Value [Member]
   
Long-term debt:    
Senior notes 1,289.1 990.3
Senior Notes $1.3 Billion [Member] | Fair Value [Member]
   
Long-term debt:    
Senior notes 1,299.9 972.5
Senior Notes $325 Million [Member] | Carrying Value [Member]
   
Long-term debt:    
Senior notes 325.0 325.0
Senior Notes $325 Million [Member] | Fair Value [Member]
   
Long-term debt:    
Senior notes 353.9 355.6
Senior Notes $400 Million [Member] | Carrying Value [Member]
   
Long-term debt:    
Senior notes 397.9 397.8
Senior Notes $400 Million [Member] | Fair Value [Member]
   
Long-term debt:    
Senior notes 430.2 422.8
Senior Notes $700 Million due 2021 [Member] | Carrying Value [Member]
   
Long-term debt:    
Senior notes 699.3  
Senior Notes $700 Million due 2021 [Member] | Fair Value [Member]
   
Long-term debt:    
Senior notes 684.0  
Carrying Value [Member]
   
Long-term receivables:    
Receivables 60.7 [1] 63.2 [1]
Long-term debt:    
Customer borrowings 5.1 4.0
Total long-term debt 3,903.9 1,717.1
Carrying Value [Member] | Customer supplemental payments [Member]
   
Long-term receivables:    
Receivables 22.3 22.3
Carrying Value [Member] | ArcelorMittal USA-Ispat receivable [Member]
   
Long-term receivables:    
Receivables 29.7 32.8
Carrying Value [Member] | Other credit receivable [Member]
   
Long-term receivables:    
Receivables 8.7 8.1
Fair Value [Member]
   
Long-term receivables:    
Receivables 63.6 [1] 66.5 [1]
Long-term debt:    
Customer borrowings 5.1 4.0
Total long-term debt 3,960.6 1,754.9
Fair Value [Member] | Customer supplemental payments [Member]
   
Long-term receivables:    
Receivables 19.9 19.5
Fair Value [Member] | ArcelorMittal USA-Ispat receivable [Member]
   
Long-term receivables:    
Receivables 35.0 38.9
Fair Value [Member] | Other credit receivable [Member]
   
Long-term receivables:    
Receivables $ 8.7 $ 8.1
[1] Includes current portion.