The amount of outstanding funds that the entity is obligated to repay.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2024-01-01
-Paragraph 55
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_55&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Definition

The amount recognised as of the acquisition date for current liabilities assumed in a business combination. [Refer: Current liabilities; Total for all business combinations [member]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 3
-IssueDate 2024-01-01
-Paragraph B64
-Subparagraph i
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=3&code=ifrs-tx-2024-en-r&anchor=para_B64_i&doctype=Appendix&subtype=B
-URIDate 2024-03-27

+ Details

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

- Definition

The current portion of non-current borrowings. [Refer: Borrowings]

+ References

+ Details

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

- Definition

The amount recognised as of the acquisition date for non-current liabilities assumed in a business combination. [Refer: Non-current liabilities; Total for all business combinations [member]]

+ References

+ Details

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

- Definition

The amount of current borrowings. [Refer: Borrowings]

+ References

+ Details

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

- References

No definition available.

+ Details

Name:	sid_ForeignDebt
Namespace Prefix:	sid_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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_LocalDebt
Namespace Prefix:	sid_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	ifrs-full_BusinessCombinationsAxis=sid_EstrelaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfFinancialAssetsAxis=sid_BondsFacilityAndACCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfFinancialAssetsAxis=sid_BNDESFINAMEFINEPDebenturesCRIAndNCEMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfAssetsAxis=sid_FixedInterestInUSDMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfAssetsAxis=sid_FixedInterestInBRLMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

BUSINESS COMBINATION (Details 2) - BRL (R$) R$ in Thousands	Dec. 31, 2025	Apr. 01, 2025	Dec. 31, 2024
IfrsStatementLineItems [Line Items]
Total Borrowings and Financing, current	R$ 10,428,559		R$ 8,821,679
Total Borrowings and Financing	R$ 53,592,620	R$ 629,856	R$ 57,558,578
Estrela [Member]
IfrsStatementLineItems [Line Items]
Foreign Debt		73,777
Local Debt		556,079
Total Borrowings and Financing, current		251,201
Total Borrowings and Financing, noncurrent		378,655
Total Borrowings and Financing		629,856
Estrela [Member] \| Bonds Facility And A C C [Member]
IfrsStatementLineItems [Line Items]
Foreign Debt		73,777
Estrela [Member] \| B N D E S F I N A M E F I N E P Debentures C R I And N C E [Member]
IfrsStatementLineItems [Line Items]
Local Debt		556,079
Estrela [Member] \| Fixed Interest In U S D [Member]
IfrsStatementLineItems [Line Items]
Current Liabilities		35,277
Non-current Liabilities		38,500
Estrela [Member] \| Fixed Interest In U S D [Member] \| Bonds Facility And A C C [Member]
IfrsStatementLineItems [Line Items]
Current Liabilities		35,277
Non-current Liabilities		38,500
Estrela [Member] \| Fixed Interest In B R L [Member]
IfrsStatementLineItems [Line Items]
Current Liabilities		215,924
Non-current Liabilities		340,155
Estrela [Member] \| Fixed Interest In B R L [Member] \| B N D E S F I N A M E F I N E P Debentures C R I And N C E [Member]
IfrsStatementLineItems [Line Items]
Current Liabilities		215,924
Non-current Liabilities		R$ 340,155