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v3.21.1

EQUITY - Reserves (Details) | 12 Months Ended
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Dec. 31, 2020
EQUITY |
Minimum legal reserve transfer as a percentage of net income | 5.00%
Maximum legal reserve balance as a percentage of total paid-in capital | 20.00%
Investments and working capital reserve, annual percentage | 5.00%

X
- Definition The percentage of annual profits which may be transferred to the Investments and Working Capital Reserve if proposed by the Board of Directors and approved by shareholders. + References No definition available. + Details
Name: | ggb_InvestmentsAndWorkingCapitalAnnualReservePercent
Namespace Prefix: | ggb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The maximum amount of legal reserves, as a percentage of total paid-in capital. + References No definition available. + Details
Name: | ggb_LegalReservesMaximumReserveBalanceAsPercentageOfTotalPaidInCapital
Namespace Prefix: | ggb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The minimum mandatory amount of earnings to be transferred into legal reserves, as a percentage of annual net income. + References No definition available. + Details
Name: | ggb_LegalReservesMinimumAnnualTransferAsPercentageOfAnnualNetIncome
Namespace Prefix: | ggb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | ifrs-full_DisclosureOfClassesOfShareCapitalAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration