The amount of total consideration in a definitive sale agreement.

No definition available.

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

- Definition

The installed capacity of hydroelectric plants.

+ References

No definition available.

+ Details

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Namespace Prefix:	ggb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of hydroelectric plants held for sale.

+ References

No definition available.

+ Details

Name:	ggb_NumberOfHydroelectricPlantsHeldForSale
Namespace Prefix:	ggb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of processing units to be sold.

+ References

No definition available.

+ Details

Name:	ggb_NumberOfProcessingUnitsToBeSold
Namespace Prefix:	ggb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Production capacity, in tons.

+ References

No definition available.

+ Details

Name:	ggb_ProductionCapacityInTons
Namespace Prefix:	ggb_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of shares authorised for repurchase by the Company.

+ References

No definition available.

+ Details

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Namespace Prefix:	ggb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Period of authorization for repurchase of shares, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	ggb_RepurchaseOfSharesAuthorizationPeriod
Namespace Prefix:	ggb_
Data Type:	xbrli:durationItemType
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 domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

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

- Definition

The amount of dividends that the company has declared but not yet paid.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 55
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_55&doctype=Standard
-URIDate 2017-03-09

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount, per share, of dividends proposed or declared before financial statements were authorised for issue but not recognised as distribution to owners.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 137
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_137_a&doctype=Standard
-URIDate 2017-03-09

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from the disposal of non-current assets or disposal groups classified as held for sale and discontinued operations. [Refer: Discontinued operations [member]; Disposal groups classified as held for sale [member]; Non-current assets or disposal groups classified as held for sale]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2017-01-01
-Paragraph 16
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2017-03-01&anchor=para_16&doctype=Standard
-URIDate 2017-03-09

+ Details

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

- Details

Name:	ifrs-full_NonadjustingEventsAfterReportingPeriodAxis=ggb_RepurchaseOfSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfShareCapitalAxis=ggb_PreferredSharesOrAmericanDepositaryReceiptsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_NonadjustingEventsAfterReportingPeriodAxis=ggb_SaleAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ProductsAndServicesAxis=ggb_SteelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_NonadjustingEventsAfterReportingPeriodAxis=ifrs-full_OtherDisposalsOfAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_NonadjustingEventsAfterReportingPeriodAxis=ggb_DividendsDeclaredMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	ifrs-full_ClassesOfShareCapitalAxis=ifrs-full_OrdinarySharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfShareCapitalAxis=ifrs-full_PreferenceSharesMember
Namespace Prefix:
Data Type:	na
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SUBSEQUENT EVENTS (Details) R$ / shares in Units, R$ in Millions, $ in Millions	Feb. 26, 2018 BRL (R$) R$ / shares	Feb. 14, 2018 BRL (R$) item	Jan. 08, 2018 shares	Jan. 31, 2018 USD ($) item T	Jan. 31, 2018 BRL (R$) item T
Repurchase of shares
SUBSEQUENT EVENTS
Authorization period			3 months
Repurchase of shares \| Preferred shares (GGBR4 ) or American Depositary Receipts (ADRs)
SUBSEQUENT EVENTS
Shares authorized for repurchase \| shares			10,000,000
Definitive sale agreement
SUBSEQUENT EVENTS
Number of processing units to be sold				2	2
Definitive sale agreement, total consideration				$ 92.5	R$ 292.5
Definitive sale agreement \| Steel
SUBSEQUENT EVENTS
Production capacity (in tons) \| T				700,000	700,000
Sale of hydroelectric plants
SUBSEQUENT EVENTS
Number of hydroelectric plants held for sale		2
Proceeds from sale of hydroelectric plants \| R$		R$ 835.0
Installed capacity (in MW)		155
Dividends declared
SUBSEQUENT EVENTS
Dividends declared \| R$	R$ 510.0
Dividends declared \| Common shares
SUBSEQUENT EVENTS
Dividends declared (in R$ per share) \| R$ / shares	R$ 0.03
Dividends declared \| Preferred shares
SUBSEQUENT EVENTS
Dividends declared (in R$ per share) \| R$ / shares	R$ 0.03