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7. INVENTORIES (Details 1) - BRL (R$) R$ in Thousands	12 Months Ended
	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.

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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.

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No definition available.

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

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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.

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No definition available.

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Name:	sid_ReversalOfInventoryWriteDownWithLowTurnoverAndObsolescence
Namespace Prefix:	sid_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration