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18. INCOME TAX AND SOCIAL CONTRIBUTION (Details 5) | 12 Months Ended
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Dec. 31, 2020
Tax losses [member] |
IncomeTaxAndSocialContributionLineItems [Line Items] |
Description | The Company incurs tax losses in the Parent Company as a result of financial expenses on its indebtedness, since it substantially holds all the loans and financing of the CSN Group. However, the Parent Company reported taxable income in two quarters of 2020.
Foreign exchange differences [member] |
IncomeTaxAndSocialContributionLineItems [Line Items] |
Description | Since 2012, the Company has opted for taxing exchange rate variations on a cash basis. As a result, taxes are due and expenses are deductible when the underlying asset or liability is settled.
Losses on Usiminas shares [member] |
IncomeTaxAndSocialContributionLineItems [Line Items] |
Description | Changes in investment in Usiminas shares are recognized on an accrual basis; however, the event that generates taxation or deductibility will only occur when the investment is sold.
Other provisions [member] |
IncomeTaxAndSocialContributionLineItems [Line Items] |
Description | Other provisions are recognized on an accrual basis and their taxation occurs only at the time of their realization, such as: provision for contingencies, loss for impairment, provision for environmental liabilities, etc.

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- Definition The description of the nature of the evidence supporting the recognition of a deferred tax asset when: (a) the utilisation of the deferred tax asset is dependent on future taxable profits in excess of the profits arising from the reversal of existing taxable temporary differences; and (b) the entity has suffered a loss in either the current or preceding period in the tax jurisdiction to which the deferred tax asset relates. [Refer: Temporary differences [member]; Deferred tax asset when utilisation is dependent on future taxable profits in excess of profits from reversal of taxable temporary differences and entity has suffered loss in jurisdiction to which deferred tax asset relates] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2020-01-01 -Paragraph 82 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2020-en-r&anchor=para_82&doctype=Standard -URIDate 2020-01-01 + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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- Details
Name: | sid_IncomeTaxAndSocialContributionAxis=sid_TaxLossesMember
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- Details
Name: | sid_IncomeTaxAndSocialContributionAxis=sid_ExchangeDifferenceExpensesMember
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Data Type: | na
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- Details
Name: | sid_IncomeTaxAndSocialContributionAxis=sid_LossesOnUsiminasSharesMember
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Data Type: | na
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- Details
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