Account receivable (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounts receivable
Additional allowances for doubtful accounts charged to statement of income	$ 34	$ 2	$ 23
Account receivable written-off	16	1	37
Customers
Accounts Receivable, Gross, Current	6,909	8,610
Allowance	(114)	(105)
Total	6,795	8,505
Denominated in Brazilian Reais
Customers
Accounts Receivable, Gross, Current	849	1,228
Denominated in other currencies, mainly US dollars
Customers
Accounts Receivable, Gross, Current	$ 6,060	$ 7,382
Steel industry accounts receivable \| Customer
Accounts receivable
Percentage of concentration risk	71.20%	70.36%

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Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

Amount of the current period expense charged against operations, the offset which is generally to the allowance for doubtful accounts for the purpose of reducing receivables, including notes receivable, to an amount that approximates their net realizable value (the amount expected to be collected).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 5

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Section S99

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-Subparagraph (SX 210.5-03.5)

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Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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The amount of decrease during the period to the valuation allowance account representing portions of such account associated with accounts receivable that have been determined to be absolutely uncollectible or that were sold or transferred, and which receivables were simultaneously written off.

+ References

No definition available.

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Amount due from customers or clients, both related and unrelated parties, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

+ References

No definition available.

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