RELATED-PARTY TRANSACTIONS - Operations with related parties (Details) R$ in Thousands	12 Months Ended
Dec. 31, 2021 BRL (R$)	Dec. 31, 2020 BRL (R$) installment	Dec. 31, 2019 BRL (R$)
Investments
RELATED PARTY TRANSACTIONS
Sales to related parties	R$ 997,298	R$ 887,945	R$ 1,572,618
Purchases from related parties	304,239	208,948	198,636
Sales to related parties, net of purchases	693,058	678,997	1,373,982
Controlling shareholders
RELATED PARTY TRANSACTIONS
Sale of property to related party		R$ 21,204
Number of annual installments \| installment		6
Rental income from related party	R$ 670	R$ 524	R$ 554
Guarantee fee percentage			0.95%
Expenses resulting from debenture guarantees			R$ 68

Reflects the guarantee fee as a percentage on the amount of debentures guaranteed.

No definition available.

Name:	ggb_DebentureGuaranteeFeePercentage
Namespace Prefix:	ggb_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The expense related to the guarantee of debentures.

+ References

No definition available.

+ Details

Name:	ggb_DebentureGuaranteeFees
Namespace Prefix:	ggb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The fair value of property sold to a related party as of the date of sale.

+ References

No definition available.

+ Details

Name:	ggb_FairValueOfSaleAgreementSaleOfPropertyToRelatedParty
Namespace Prefix:	ggb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The net revenue (purchases) from transactions with related parties.

+ References

No definition available.

+ Details

Name:	ggb_NetRevenuePurchasesFromTransactionsWithRelatedParties
Namespace Prefix:	ggb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The number of annual installments over which payments are to be received under the terms of agreement in the sale of property.

+ References

No definition available.

+ Details

Name:	ggb_NumberOfAnnualInstallmentsSaleOfProperty
Namespace Prefix:	ggb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of rental income resulting from agreements with a related party.

+ References

No definition available.

+ Details

Name:	ggb_RentalIncomeRelatedParty
Namespace Prefix:	ggb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

+ References

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of goods purchased by the entity in related party transactions. [Refer: Related parties [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 24
-IssueDate 2021-01-01
-Paragraph 21
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=24&code=ifrs-tx-2021-en-r&anchor=para_21_a&doctype=Standard
-URIDate 2021-03-24

+ Details

Name:	ifrs-full_PurchasesOfGoodsRelatedPartyTransactions
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of revenue arising from the sale of goods in related party transactions. [Refer: Revenue; Related parties [member]]

+ References

+ Details

Name:	ifrs-full_RevenueFromSaleOfGoodsRelatedPartyTransactions
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=ifrs-full_InvestmentsAccountedForUsingEquityMethodMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=ggb_ControllingShareholdersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: