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

No definition available.

Name:	ggb_BorrowingsExcludingNotesAndDebentures
Namespace Prefix:	ggb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

No definition available.

+ Details

Name:	ggb_IfrsDebtInstrumentFaceAmount
Namespace Prefix:	ggb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

No definition available.

+ Details

Name:	ggb_IfrsLineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	ggb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Average amount borrowed under the credit facility during the period.

+ References

No definition available.

+ Details

Name:	ggb_LineOfCreditFacilityOutstandingAmount
Namespace Prefix:	ggb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of bilateral loans early settled.

+ References

No definition available.

+ Details

Name:	ggb_NumberOfBilateralLoansEarlySettled
Namespace Prefix:	ggb_
Data Type:	xbrli:integerItemType
Balance Type:	na
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_DisclosureOfDetailedInformationAboutBorrowingsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow to settle borrowings, classified as financing activities. [Refer: Borrowings]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 7
-IssueDate 2021-01-01
-Paragraph 17
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2021-en-r&anchor=para_17_d&doctype=Standard
-URIDate 2021-03-24

+ Details

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

- Details

Name:	ifrs-full_BorrowingsByNameAxis=ggb_WorkingCapitalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_BorrowingsByNameAxis=ggb_GlobalCreditLineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

SHORT-TERM DEBT AND LONG-TERM DEBT - Additional disclosures (Details) R$ in Thousands, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2021 BRL (R$)	Dec. 31, 2021 BRL (R$)	Dec. 31, 2020 BRL (R$)	Dec. 31, 2019 BRL (R$)	Dec. 31, 2021 USD ($)	Oct. 31, 2019 BRL (R$)
LOANS AND FINANCING
Loans and financing	R$ 11,109,786	R$ 11,109,786	R$ 14,612,934
Principal amount	2,208,000	2,208,000			$ 395.8
IFRS, Debt Instrument, Face Amount	R$ 2,208,000	2,208,000			395.8
Number of Bilateral Loans Early Settled	2
Repayments of borrowings, classified as financing activities	R$ 775,000	5,116,621	5,084,028	R$ 4,885,083
Working capital
LOANS AND FINANCING
Loans and financing	480,905	480,905	R$ 1,178,557
Global Credit Line
LOANS AND FINANCING
Amount of outstanding balance credit facility	474,000	474,000			$ 85.0
Maximum borrowing capacity	R$ 4,464,000	R$ 4,464,000				R$ 800,000