INCOME TAX AND SOCIAL CONTRIBUTION (Details 1) - BRL (R$) R$ in Thousands	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
IfrsStatementLineItems [Line Items]
Profit before income tax and social contribution	R$ (1,679,518)	R$ (1,543,349)	R$ 1,035,367
Tax rate	34.00%	34.00%	34.00%
Income tax and social contribution at combined statutory rate	R$ 571,036	R$ 524,739	R$ (352,025)
Income tax and social contribution in net income for the year	R$ 172,792	R$ 5,208	R$ (632,718)
Effective tax rate	10.00%	0.00%	61.00%
Equity In Results Of Affiliated Companies [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	R$ 1,014,282	R$ 188,205	R$ 178,978
Effect Of Differentiated Rates And Tax Exempt Profits In Investments [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	(1,209,761)	(814,713)	(181,409)
Transfer Pricing Adjustment And Profits Abroad [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	(70,837)	(67,580)	(91,883)
Income Tax And Social Contribution On Foreign Profit [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	7,172	10,200	131,836
Indebtdness Limit [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	(10,384)
Tax Incentives [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	65,013	102,087	71,756
Interest On Equity [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	87,912	79,282	47,315
Recognition Reversal Of Tax Credits [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	(64,690)	(62,088)	(337,239)
Reversal For Deferred Income Tax And Social Contribution Credit [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	(188,975)
Other Permanent Deductions Additions [Member]
IfrsStatementLineItems [Line Items]
Adjustment to reflect the effective rate	R$ (27,976)	R$ 45,076	R$ (100,047)

The amount of profit (loss) for a period before deducting tax expense. [Refer: Profit (loss)]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2024-01-01
-Paragraph 81
-Subparagraph c
-Clause i
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=12&code=ifrs-tx-2024-en-r&anchor=para_81_c_i&doctype=Standard
-URIDate 2024-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2024-01-01
-Paragraph 81
-Subparagraph c
-Clause ii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=12&code=ifrs-tx-2024-en-r&anchor=para_81_c_ii&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Definition

The applicable income tax rate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2024-01-01
-Paragraph 81
-Subparagraph c
-Clause ii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=12&code=ifrs-tx-2024-en-r&anchor=para_81_c_ii&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_ApplicableTaxRate
Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that the entity does not separately disclose in the same statement or note. [Refer: Accounting profit; Applicable tax rate]

+ References

+ Details

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

- Definition

The product of the accounting profit multiplied by the applicable tax rate(s). [Refer: Accounting profit; Applicable tax rate]

+ References

+ Details

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

- Definition

The tax rate effect on the reconciliation between the average effective tax rate and the applicable tax rate resulting from tax losses. [Refer: Average effective tax rate; Applicable tax rate]

+ References

+ Details

Name:	ifrs-full_TaxRateEffectOfTaxLosses
Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:percentItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	sid_IfrsStatementLineItems
Namespace Prefix:	sid_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	sid_IncomeTaxExpenseContinuingOperations1
Namespace Prefix:	sid_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_EquityInResultsOfAffiliatedCompaniesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_EffectOfDifferentiatedRatesAndTaxExemptProfitsInInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_TransferPricingAdjustmentAndProfitsAbroadMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_IncomeTaxAndSocialContributionOnForeignProfitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_IndebtdnessLimitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_TaxIncentivesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_InterestOnEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_RecognitionReversalOfTaxCreditsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_ReversalForDeferredIncomeTaxAndSocialContributionCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	sid_IncomeTaxAndSocialContributionAxis=sid_OtherPermanentDeductionsAdditionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: