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7. INVENTORIES (Details 1) - BRL (R$) R$ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Inventories [Abstract] |  |
Opening balance | R$ (134,553) | R$ (157,754)
(Estimated losses) / Reversal of inventories with low turnover and obsolescence | 25,515 | 23,201
Closing balance | R$ (109,038) | R$ (134,553)

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

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- Definition The amount represents beginning balance of inventory. + References No definition available. + Details
Name: | sid_InventoryNetOne
Namespace Prefix: | sid_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition The amount recognised as a reduction in the amount of inventories recognised as an expense due to the reversal low turnover and obsolescence. + References No definition available. + Details
Name: | sid_ReversalOfInventoryWriteDownWithLowTurnoverAndObsolescence
Namespace Prefix: | sid_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration