XML 154 R131.htm IDEA: XBRL DOCUMENT
v3.19.1

EMPLOYEE BENEFITS - Defined benefit pension plan - Assumptions used to calculate defined benefit plans (Details) - Defined benefit pension plan | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Brazil |  |
Summary of assumptions used to calculate the defined benefit plans |  |
Average discount rate | 9.10% | 9.84%
North America |  |
Summary of assumptions used to calculate the defined benefit plans |  |
Rate of increase in compensation | 3.00% | 3.00%
North America | Minimum |  |
Summary of assumptions used to calculate the defined benefit plans |  |
Average discount rate | 3.50% | 3.25%
North America | Maximum |  |
Summary of assumptions used to calculate the defined benefit plans |  |
Average discount rate | 4.25% | 4.25%

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

X
- Definition The discount rate used as the significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 144 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_144&doctype=Standard -URIDate 2018-03-16 + Details
Name: | ifrs-full_ActuarialAssumptionOfDiscountRates
Namespace Prefix: | ifrs-full_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The expected rate of salary increases used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 144 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_144&doctype=Standard -URIDate 2018-03-16 + Details
Name: | ifrs-full_ActuarialAssumptionOfExpectedRatesOfSalaryIncreases
Namespace Prefix: | ifrs-full_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | ifrs-full_DefinedBenefitPlansAxis=ifrs-full_DefinedBenefitPlansOtherThanMultiemployerPlansStatePlansAndPlansThatShareRisksBetweenEntitiesUnderCommonControlMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_BR
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=srt_NorthAmericaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |