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Quarterly report pursuant to Section 13 or 15(d)

Fair Value Of Financial Instruments (Carrying Value And Fair Value Of Financial Instruments Disclosure) (Detail)

v2.4.0.6
Fair Value Of Financial Instruments (Carrying Value And Fair Value Of Financial Instruments Disclosure) (Detail) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Long-term debt: Ìý Ìý
Long-term debt noncurrent fair value $ 3,614.1 $ 3,608.7
Fair Value [Member]
Ìý Ìý
Receivables: Ìý Ìý
Receivables 46.8 61.5
Long-term debt: Ìý Ìý
Revolving loan 325.0 Ìý
Long-term debt noncurrent fair value 3,976.1 3,820.5
Fair Value [Member] | Customer Supplemental Payments [Member]
Ìý Ìý
Receivables: Ìý Ìý
Receivables 10.5 20.8
Fair Value [Member] | ArcelorMittal USA - Receivable [Member]
Ìý Ìý
Receivables: Ìý Ìý
Receivables 26.2 30.7
Fair Value [Member] | Other Credit Receivable [Member]
Ìý Ìý
Receivables: Ìý Ìý
Receivables 10.1 10.0
Carrying Value [Member]
Ìý Ìý
Receivables: Ìý Ìý
Receivables 44.2 58.8
Long-term debt: Ìý Ìý
Revolving loan 325.0 Ìý
Long-term debt noncurrent fair value 3,614.1 3,608.7
Carrying Value [Member] | Customer Supplemental Payments [Member]
Ìý Ìý
Receivables: Ìý Ìý
Receivables 11.1 22.3
Carrying Value [Member] | ArcelorMittal USA - Receivable [Member]
Ìý Ìý
Receivables: Ìý Ìý
Receivables 23.0 26.5
Carrying Value [Member] | Other Credit Receivable [Member]
Ìý Ìý
Receivables: Ìý Ìý
Receivables 10.1 10.0
Term Loan - $1.25 Billion [Member] | Fair Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Term loan 847.3 897.2
Term Loan - $1.25 Billion [Member] | Carrying Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Term loan 847.3 897.2
Senior Notes - $700 Million [Member] | Fair Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Senior notes 753.8 726.4
Senior Notes - $700 Million [Member] | Carrying Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Senior notes 699.4 699.3
Senior Notes - $1.3 Billion [Member] | Fair Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Senior notes 1,526.4 1,399.4
Senior Notes - $1.3 Billion [Member] | Carrying Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Senior notes 1,289.3 1,289.2
Senior Notes - $400 Million [Member] | Fair Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Senior notes 461.5 448.8
Senior Notes - $400 Million [Member] | Carrying Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Senior notes 398.1 398.0
Senior Notes - $55 Million [Member] | Fair Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Senior notes 62.1 348.7
Senior Notes - $55 Million [Member] | Carrying Value [Member]
Ìý Ìý
Long-term debt: Ìý Ìý
Senior notes $ 55.0 $ 325.0