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14 INCOME TAX AND SOCIAL CONTRIBUTION (Details 5) | 12 Months Ended
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Dec. 31, 2019
Tax losses [Member] |
IncomeTaxAndSocialContributionTillLineItems [Line Items] |
Description | The Company incur tax losses at the parent company level, because of financial expenses over its leverage, since it holds substantially all loans and financings of CSN group. In 2018 the parent company presented taxable income.
Foreign exchange differences [Member] |
IncomeTaxAndSocialContributionTillLineItems [Line Items] |
Description | The Company usually opts for the taxation of exchange differences on a cash basis. As a result, taxes are due and expenses are deductible when the underlying asset or liabilities is settled.
Losses on Usiminas shares [Member] |
IncomeTaxAndSocialContributionTillLineItems [Line Items] |
Description | Changes in investments in Usiminas’ shares are recognized on an accrual basis, but the event that generates taxation or deductibility will only occur at the time of divestment.
Other provisions [Member] |
IncomeTaxAndSocialContributionTillLineItems [Line Items] |
Description | Other provisions are recognized on an accrual basis, but their taxation occurs only at the time of their realization. This includes provisions for contingencies, impairment losses, 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 2019-01-01 -Paragraph 82 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_82&doctype=Standard -URIDate 2019-03-27 + 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
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Data Type: | na
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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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Data Type: | na
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