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10. BASIS OF CONSOLIDATION AND INVESTMENTS IN SUBSIDIARIES AND AFFILIATES (Details) - shares | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 1,387,524,047 | 1,387,524,047
Diplic II- Fundo de investimento multimercado credito privado [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interest (%), exclusive funds |  | 100.00% | 100.00%
Core business |  | Investment fund |
Caixa Vertice - Fundo de investimento multimercado credito privado [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interest (%), exclusive funds |  | 100.00% | 100.00%
Core business |  | Investment fund |
VR1 - Fundo de investimento multimercado credito privado [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interest (%), exclusive funds |  | 100.00% | 100.00%
Core business |  | Investment fund |
Arvedi Metalfer do Brasil S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 49,074,882 |
Equity interest (%), associate |  | 20.00% | 20.00%
Core business |  | Metallurgy and Equity interests |
Ita Energetica S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 253,606,846 |
Equity interests (%), operation |  | 48.75% | 48.75%
Core business |  | Electric power generation |
CONSORCIO DA USINA HIDRELETRICA DE IGARAPAVA [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), operation |  | 17.92% | 17.92%
Core business |  | Electric power consortium |
MRS Logistica S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) | [1] | 63,377,198 |
Equity interest (%), joint venture | [1] | 18.64% | 18.64%
Core business | [1] | Railroad transportation |
Aceros Del Orinoco S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interest (%), joint venture |  | 31.82% | 31.82%
Core business |  | Dormant company |
Transnordestina logistica s.a [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) | [2] | 24,670,093 |
Equity interest (%), joint venture | [2] | 47.26% | 47.26%
Core business | [2] | Railroad logistics |
Equimac S.A [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) | [3] | 1,117 |
Equity interest (%), joint venture | [3] | 50.00% |
Core business | [3] | Rental of commercial and industrial machinery and equipment |
MRS Logistica S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interest (%), joint venture | [1] | 16.30% | 16.30%
Core business | [1] | Railroad transportation |
CSN Islands VII Corp. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 20,001,000 |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Financial transactions |
CSN inova ventures [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) | [4] | 50,000 |
Equity interests (%), subsidiary | [4] | 100.00% | 100.00%
Core business | [4] | Financial transactions |
CSN Islands XII Corp. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 1,540 |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Financial transactions |
CSN Steel S.L.U. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 22,042,688 |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Equity interests and Financial transactions |
TdBB S.A [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) | [5] |  |
Equity interests (%), subsidiary | [5] | 100.00% | 100.00%
Core business | [5] | Equity interests |
Sepetiba Tecon S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 254,015,052 |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Port services |
Minerios nacional s.a. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 141,719,295 |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Mining and Equity interests |
Companhia Florestal do Brasil [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 66,354,391 |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Reforestation |
Estanho de Rondonia S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 195,454,162 |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Tin Mining |
Companhia Metalurgica Prada [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 555,142,354 |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Manufacture of containers and distribution of steel products |
CSN Mineracao SA [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 158,419,480 |
Equity interests (%), subsidiary |  | 87.52% | 87.52%
Core business |  | Mining |
CSN Energia S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 43,149 |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Sale of electric power |
FTL - FERROVIA TRANSNORDESTINA LOGISTICA SA ("FTL") [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 486,592,830 |
Equity interests (%), subsidiary |  | 92.38% | 92.38%
Core business |  | Railroad logistics |
Nordeste Logistica S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 99,999 |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Port services |
CSN Inova Ltd. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  |  |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Advisory and implementation of new development projec |
CSN Equipamentos S.A [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) | [3] |  |
Equity interests (%), subsidiary | [3] |  | 99.99%
Core business | [3] | Rental of commercial and industrial machinery and equipment |
CBSI - Companhia Brasileira de Servicos de Infraestrutura [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) |  | 4,669,986 |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Equity interests and product sales and iron ore |
CSN Cimentos S.A [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) | [6] | 90 |
Equity interests (%), subsidiary | [6] | 90.00% |
Core business | [6] | Manufacturing and sale of cement |
Lusosider Projectos Siderurgicos S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Equity interests and product sales |
Lusosider Acos Planos, S. A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Steel and Equity interests |
CSN Resources S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Financial transactions and Equity interests |
Companhia Brasileira de Latas [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 99.99% | 99.99%
Core business |  | Sale of cans and containers in general and Equity interests |
Companhia de Embalagens Metalicas MMSA [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 99.67% | 99.67%
Core business |  | Production and sale of cans and related activities |
Companhia de Embalagens Metalicas - MTM [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 99.67% | 99.67%
Core business |  | Production and sale of cans and related activities |
CSN Steel Holdings 1, S.L.U. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Financial transactions, product sales and Equity interests |
CSN Productos Siderurgicos S.L. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Financial transactions, product sales and Equity interests |
Stalhwerk Thuringen GmbH [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Production and sale of long steel and related activities |
CSN Steel Sections UK Limited [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary | [7] |  | 100.00%
Core business | [7] | Sale of long steel |
CSN Steel Sections Polska Sp.Z.o.o [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Financial transactions, product sales and Equity interests |
CSN Mining Holding, S.L [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 87.52% | 87.52%
Core business |  | Financial transactions, product sales and Equity interests |
CSN Mining GmbH [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 87.52% | 87.52%
Core business |  | Financial transactions, product sales and Equity interests |
CSN Mining Asia Limited [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 87.52% | 87.52%
Core business |  | Commercial representation |
Lusosider Iberica S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Steel, commercial and industrial activities and equity interests |
CSN Mining Portugal, Unipessoal Lda. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 87.52% | 87.52%
Core business |  | Commercial and representation of products |
Companhia Siderurgica Nacional, LLC [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Equity interests (%), subsidiary |  | 100.00% | 100.00%
Core business |  | Import and distribution/resale of products |
CSN Cimentos S.A. [member] |  |  |
BasisOfConsolidationAndInvestmentsInSubsidiariesAndAffiliatesLineItems [Line Items] |  |  |
Number of shares held by CSN (in units) | [6] | 10 |
Equity interests (%), subsidiary | [6] | 10.00% |
Core business | [6] | Manufacturing and sale of cement |
[1] | As of December 31, 2020, the Company directly held 63,377,198 shares, of which 26,611,282 were common and 36,765,916 were preferred, and indirectly 63,338,872 shares, of which 25,802,872 were common and 37,536,000 were preferred
[2] | As of December 31, 2020, the Company had 24,168,304 common shares and 501,789 Class B preferred shares.
[3] | On June 26, 2020, CSN Equipamentos SA had its corporate name changed to Equimac SA and its capital increased by Unidas Guindastes Eireli. With this capital increase, CSN's stake in Equimac's share capital increased to 50% and was classified as joint venture.
[4] | On June 29, 2020, CSN Islands XI Corp. changed its corporate name to CSN Inova Ventures.
[5] | Dormant companies.
[6] | Company acquired on October 2, 2020.
[7] | Company liquidated on March 11, 2020.

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