TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS - Tax contingencies (Details) - BRL (R$) R$ in Thousands	Dec. 31, 2022	Dec. 02, 2019
Gerdau Acominas S.A., Gerdau Acos Longos S.A., and Gerdau Acos Especiais S.A. \| Goodwill Deductibility \| Administrative collection
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	R$ 8,734,573
Gerdau Acos Longos S.A. and Gerdau Acominas S.A. \| Goodwill Deductibility \| Voluntary Appeal, Filed
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	5,755,883
Gerdau Acos Longos S.A. \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	547,501
Gerdau Acos Longos S.A. \| Goodwill Deductibility \| Awaiting judgement, lower court
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	5,597
Gerdau Acos Longos S.A. \| Goodwill Deductibility \| Awaiting Judgement, Embargoes to Tax Enforcement
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	89,684
Gerdau Acos Longos S.A. \| Goodwill Deductibility \| Superior Chamber of Tax Appeals
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	192,076
Gerdau Acos Longos S.A. \| Goodwill Deductibility \| Embargo to Enforcement, Filed
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	432,894
Gerdau Acos Longos S.A. \| Goodwill Deductibility \| Motion for clarification filed
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	319,983
Gerdau Acos Longos S.A. \| Goodwill Deductibility \| Notice of judgment received
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	344,171
Gerdau Acos Longos S.A. \| Goodwill Deductibility \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	623,485
Gerdau Acos Longos S.A. \| Goodwill Deductibility \| Voluntary Appeal, Filed
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	155,962
Gerdau Acos Especiais S.A. \| Goodwill Deductibility \| Special Appeal, Filed
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	119,305
Gerdau Acos Especiais S.A. \| Goodwill Deductibility \| Special appeal, pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	148,032
Tax contingencies \| IPI credit on inputs \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	434,095
Tax contingencies \| Non-approval of compensation of credits on inputs \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	1,646,717
Tax contingencies \| Social security contributions. \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	139,219
Tax contingencies \| Other Taxes \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	732,283
Tax contingencies \| Goodwill Deductibility \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	513,287	R$ 164,879
Tax contingencies \| Goodwill Deductibility \| Special Appeal, Filed
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	27,325
Tax contingencies \| Goodwill Deductibility \| Voluntary Appeal, Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	234,846
Tax contingencies \| Goodwill Deductibility \| Voluntary Appeal, Filed
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	86,237
Tax contingencies \| Gerdau Acos Longos S.A. and Gerdau Acominas S.A. \| ICMS (State Value Added Tax) \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	559,076
Tax contingencies \| Gerdau Acos Longos S.A. \| Withholding Income Tax
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	1,719,027
Tax contingencies \| Gerdau Acos Longos S.A. \| Withholding Income Tax \| Administrative processing
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	1,069,274
Tax contingencies \| Gerdau Acos Longos S.A. \| Withholding Income Tax \| Superior Chamber of Tax Appeals
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	649,753
Tax contingencies \| Gerdau Internacional Empreendimentos Ltda. and Gerdau Acos Especiais S.A \| IRPJ - Corporate Income Tax and CSLL - Social Contribution Tax [Member] \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	1,346,502
Tax contingencies \| Gerdau Internacional Empreendimentos Ltda \| Corporate Income Tax and Social Contribution Tax \| Pending
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	1,107,520
Tax contingencies \| Gerdau Acos Especiais S.A. \| Corporate Income Tax and Social Contribution Tax \| First instance, awaiting judgement of the Tax Enforcement Embargoes
TAX, CIVIL AND LABOR CLAIMS AND CONTINGENT ASSETS
Estimated financial effect of contingent liabilities	R$ 238,892