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LOANS AND FINANCING - Additional Disclosures (Details) R$ in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2019 BRL (R$)	Nov. 30, 2019 USD ($)	Oct. 31, 2019 BRL (R$)	Dec. 31, 2018 BRL (R$)
LOANS AND FINANCING
Loans and financing		R$ 13,138,823			R$ 13,367,841
Notional value		12,958,565			R$ 13,178,457
Gerdau Aominas
LOANS AND FINANCING
Amount of outstanding balance credit facility	$ 70	282,000
GUSAP III LP
LOANS AND FINANCING
Bonds issued		2,015,000	$ 500
Global Credit Line
LOANS AND FINANCING
Loans and financing		241,800
Amount of outstanding balance credit facility		60,000
Maximum borrowing capacity		R$ 3,224,000		R$ 800,000

X

- Definition

The amount of outstanding funds that the entity is obligated to repay, excluding notes and debentures.

+ References

No definition available.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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- Definition

Average amount borrowed under the credit facility during the period.

+ References

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X

- Definition

The amount of bonds issued by the entity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 112
-Subparagraph c
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Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

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- Definition

The nominal or face amount of a financial instrument, used to calculate payments made on that instrument.

+ References

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-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 112
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