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10. BASIS OF CONSOLIDATION AND INVESTMENTS IN SUBSIDIARIES AND AFFILIATES (Details 7)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Buildings and infrastructure [member]
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items]
Useful lives	27 years	21 years

X

- Definition

The useful life, measured as period of time, used for property, plant and equipment. [Refer: Property, plant and equipment]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 16
-IssueDate 2020-01-01
-Paragraph 73
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2020-en-r&anchor=para_73_c&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_UsefulLifeMeasuredAsPeriodOfTimePropertyPlantAndEquipment
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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

X

- Details

Name:	ifrs-full_TypesOfInvestmentPropertyAxis=ifrs-full_BuildingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: