NATIONAL STEEL CO (SEC Filing Page | XBRL Cloud Viewer | XBRL Instance)

Line	Label	Object Class	Period Type	Balance	Report ElementName
1	00000001 - Document - Document and Entity Information	Network	*	*	http://csn.com.br/role/DocumentAndEntityInformation
2	Implied Table	Table	*	*	implied:Table
3	Document And Entity Information	Abstract			SID:DocumentAndEntityInformationAbstract
4	Entity Registrant Name	Concept (Text/String)	For Period		dei:EntityRegistrantName
5	Entity Central Index Key	Concept (CIK Number)	For Period		dei:EntityCentralIndexKey
6	Document Type	Concept (Submission Type)	For Period		dei:DocumentType
7	Document Period End Date	Concept (Date)	For Period		dei:DocumentPeriodEndDate
8	Amendment Flag	Concept (Yes/No)	For Period		dei:AmendmentFlag
9	Current Fiscal Year End Date	Concept (Month/Day)	For Period		dei:CurrentFiscalYearEndDate
10	Entity a Well-known Seasoned Issuer	Concept (Yes/No)	For Period		dei:EntityWellKnownSeasonedIssuer
11	Entity a Voluntary Filer	Concept (Yes/No)	For Period		dei:EntityVoluntaryFilers
12	Entity's Reporting Status Current	Concept (Yes/No)	For Period		dei:EntityCurrentReportingStatus
13	Entity Filer Category	Concept (Filer Category)	For Period		dei:EntityFilerCategory
14	Entity Emerging Growth Company	Concept (Yes/No)	For Period		dei:EntityEmergingGrowthCompany
15	Entity Shell Company	Concept (Yes/No)	For Period		dei:EntityShellCompany
16	Entity Public Float	Concept (Monetary)	As Of	Credit	dei:EntityPublicFloat
17	Entity Common Stock, Shares Outstanding	Concept (Shares)	As Of		dei:EntityCommonStockSharesOutstanding
18	Document Fiscal Period Focus	Concept (Fiscal Period)	For Period		dei:DocumentFiscalPeriodFocus
19	Document Fiscal Year Focus	Concept (Year)	For Period		dei:DocumentFiscalYearFocus
20	00000002 - Statement - Consolidated Balance Sheet	Network	*	*	http://csn.com.br/role/BalanceSheet
21	Implied Table	Table	*	*	implied:Table
22	Statement of financial position [abstract]	Abstract			ifrs-full:StatementOfFinancialPositionAbstract
23	Assets	Abstract			ifrs-full:AssetsAbstract
24	CURRENT ASSETS	Abstract			ifrs-full:CurrentAssetsAbstract
25	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
26	Financial Investments measured at amortized cost	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentAccountedForUsingEquityMethod
27	Trade receivables	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentTradeReceivables
28	Inventories	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
29	Other current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentNonfinancialAssets
30	Total current assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssets
31	NON-CURRENT ASSETS	Abstract			ifrs-full:NoncurrentAssetsAbstract
32	Deferred income taxes	Concept (Monetary)	As Of	Debit	ifrs-full:DeferredTaxAssets
33	Other non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentNonfinancialAssets
34	Financial Investments measured at amortized cost	Concept (Monetary)	As Of	Debit	ifrs-full:FairValueOfFinancialAssetsReclassifiedAsMeasuredAtAmortisedCost
35	Total	Concept (Monetary)	As Of	Debit	SID:NoncurrentAssetsSubtotal
36	Investments in associates and joint controlled entities	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentsInSubsidiariesJointVenturesAndAssociates
37	Property, plant and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
38	Intangible assets	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsAndGoodwill
39	Total non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentAssets
40	TOTAL ASSETS	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
41	Liabilities and shareholders' equity	Abstract			ifrs-full:EquityAndLiabilitiesAbstract
42	CURRENT LIABILITIES	Abstract			ifrs-full:CurrentLiabilitiesAbstract
43	Payroll and related taxes	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentAccruedExpensesAndOtherCurrentLiabilities
44	Trade payables	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherCurrentPayables
45	Taxes payable	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentTaxLiabilities
46	Borrowings and financing	Concept (Monetary)	As Of	Credit	ifrs-full:ShorttermBorrowings
47	Other payables	Concept (Monetary)	As Of	Credit	ifrs-full:OtherCurrentPayables
48	Provisions for tax, social security, labor and civil risks	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentProvisions
49	Total current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLiabilities
50	NON-CURRENT LIABILITIES	Abstract			ifrs-full:NoncurrentLiabilitiesAbstract
51	Borrowings and financing	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
52	Other payables	Concept (Monetary)	As Of	Credit	ifrs-full:OtherNoncurrentPayables
53	Deferred income taxes	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilities
54	Provisions for tax, social security, labor and civil risks	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentProvisions
55	Pension and healthcare plan	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentProvisionsForEmployeeBenefits
56	Provision for environmental liabilities and decommissioning of assets	Concept (Monetary)	As Of	Credit	ifrs-full:OtherLongtermProvisions
57	Total non-current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentLiabilities
58	Shareholders' Equity	Abstract			ifrs-full:EquityAbstract
59	Issued capital	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
60	Capital reserves	Concept (Monetary)	As Of	Credit	ifrs-full:CapitalReserve
61	Legal reserves	Concept (Monetary)	As Of	Credit	ifrs-full:StatutoryReserve
62	Earnings reserves	Concept (Monetary)	As Of	Credit	ifrs-full:OtherReserves
63	Treasury Shares	Concept (Monetary)	As Of	Debit	ifrs-full:TreasuryShares
64	Accumulated Profit / (Loss)	Concept (Monetary)	As Of	Credit	ifrs-full:RetainedEarnings
65	Other comprehensive income	Concept (Monetary)	As Of	Credit	ifrs-full:AccumulatedOtherComprehensiveIncome
66	Total equity attributable to owners of the Company	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAttributableToOwnersOfParent
67	Non-controlling interests	Concept (Monetary)	As Of	Credit	ifrs-full:NoncontrollingInterests
68	Total equity	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
69	TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAndLiabilities
70	00000003 - Statement - Consolidated Statements of Income	Network	*	*	http://csn.com.br/role/StatementsOfIncome
71	Implied Table	Table	*	*	implied:Table
72	Profit or loss [abstract]	Abstract			ifrs-full:IncomeStatementAbstract
73	Revenues from sale of goods and rendering of services	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
74	Cost of sales and services	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
75	Gross profit	Concept (Monetary)	For Period	Credit	ifrs-full:GrossProfit
76	Operating expenses/income	Concept (Monetary)	For Period	Credit	ifrs-full:OtherOperatingIncomeExpense
77	Selling expenses	Concept (Monetary)	For Period	Debit	ifrs-full:SalesAndMarketingExpense
78	General and administrative expenses	Concept (Monetary)	For Period	Debit	ifrs-full:AdministrativeExpense
79	Other operating income	Concept (Monetary)	For Period	Credit	ifrs-full:MiscellaneousOtherOperatingIncome
80	Other operating expenses	Concept (Monetary)	For Period	Debit	ifrs-full:MiscellaneousOtherOperatingExpense
81	Equity in results of affiliated companies	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfAssociatesAndJointVenturesAccountedForUsingEquityMethod
82	Profit before financial income (expenses) and taxes	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromOperatingActivities
83	Financial income	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncome
84	Financial expenses	Concept (Monetary)	For Period	Debit	ifrs-full:FinanceCosts
85	Profit (loss) before taxes	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
86	Income tax and social contribution	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
87	Profit (Loss) from continued operations	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromContinuingOperations
88	Profit (Loss) from discontinued operations	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromDiscontinuedOperations
89	Profit (loss) for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
90	Profit (Loss) for the year attributed to:	Abstract			ifrs-full:ProfitLossAbstract
91	Controlling interests	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOwnersOfParent
92	Non-controlling interests	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToNoncontrollingInterests
93	Earnings (loss) per common share - (reais/share)	Abstract			ifrs-full:EarningsPerShareAbstract
94	Basic	Concept (Share)	For Period		ifrs-full:BasicEarningsLossPerShare
95	Diluted	Concept (Share)	For Period		ifrs-full:DilutedEarningsLossPerShare
96	00000004 - Statement - Consolidated Statements of Comprehensive Income	Network	*	*	http://csn.com.br/role/StatementsOfComprehensiveIncome
97	Implied Table	Table	*	*	implied:Table
98	Statement of comprehensive income [abstract]	Abstract			ifrs-full:StatementOfComprehensiveIncomeAbstract
99	Profit (loss) for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
100	Items that will not be subsequently reclassified to the statement of income	Abstract			ifrs-full:ComponentsOfOtherComprehensiveIncomeThatWillNotBeReclassifiedToProfitOrLossNetOfTaxAbstract
101	Actuarial (losses)/gains on defined benefit plan from investments in subsidiaries	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxGainsLossesFromInvestmentsInEquityInstruments
102	Actuarial (losses)/gains on defined benefit pension plan	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxGainsLossesOnRemeasurementsOfDefinedBenefitPlans
103	Income tax and social contribution on actuarial (losses) gains on defined benefit pension plan	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToRemeasurementsOfDefinedBenefitPlansOfOtherComprehensiveIncome
104	Items that will not be subsequently reclassified to the statement of income	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeThatWillNotBeReclassifiedToProfitOrLossNetOfTax
105	Items that could be subsequently reclassified to the statement of income	Abstract			ifrs-full:ComponentsOfOtherComprehensiveIncomeThatWillBeReclassifiedToProfitOrLossNetOfTaxAbstract
106	Cumulative translation adjustments for the year	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationNetOfTax
107	Fair Value through other comprehensive income	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnRemeasuringAvailableforsaleFinancialAssetsNetOfTax
108	(Loss)/Gain on percentage change in percentage of investments	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnChangeInValueOfTimeValueOfOptionsNetOfTax
109	(Loss) gain on cash flow hedge accounting	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnCashFlowHedgesNetOfTax
110	Cash Flow hedge reclassified to income statement	Concept (Monetary)	For Period	Debit	ifrs-full:ReclassificationAdjustmentsOnCashFlowHedgesNetOfTax
111	(Loss) /gain on hedge of net investments in foreign subsidiaries	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnHedgesOfNetInvestmentsInForeignOperationsNetOfTax
112	(Loss) / gain on business combination	Concept (Monetary)	For Period	Credit	SID:LossGainOnBusinessCombination
113	Items that could be subsequently reclassified to the statement of income	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeThatWillBeReclassifiedToProfitOrLossNetOfTax
114	Other comprehensive income	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncome
115	Comprehensive income (loss) for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
116	Attributable to:	Abstract			ifrs-full:ComprehensiveIncomeAttributableToAbstract
117	Attributed to owners of the Company	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncomeAttributableToOwnersOfParent
118	Attributed to non-controlling interests	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncomeAttributableToNoncontrollingInterests
119	00000005 - Statement - Consolidated Statements of Cash Flows	Network	*	*	http://csn.com.br/role/StatementsOfCashFlows
120	Implied Table	Table	*	*	implied:Table
121	Statement of cash flows [abstract]	Abstract			ifrs-full:StatementOfCashFlowsAbstract
122	Profit (loss) for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
123	Adjustments to reconcile net income (loss) to net cash provided by operations	Abstract			ifrs-full:AdjustmentsForReconcileProfitLossAbstract
124	Accrued charges on borrowings and financing	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForFinanceCosts
125	Charges on loans and financing granted	Concept (Monetary)	For Period	Debit	ifrs-full:OtherAdjustmentsToReconcileProfitLoss
126	Depreciation/ depletion / amortization	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDepreciationAndAmortisationExpense
127	Equity in results of affiliated companies	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfAssociatesAccountedForUsingEquityMethod
128	Deferred income tax and social contribution	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDeferredTaxExpense
129	Provision for tax, social security, labor and civil risks	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForProvisions
130	Monetary variations and exchange differences	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForUnrealisedForeignExchangeLossesGains
131	Gain/(Loss) of derivative financial instruments	Concept (Monetary)	For Period	Debit	SID:AdjustmentsForProvisionsOfSwapsForwardsTransactions
132	Eletrobras's compulsory loan	Concept (Monetary)	For Period	Debit	SID:MonetaryAdjustmentRelatedToEletrobrssCompulsoryLoan
133	Proceeds from disposal of fixed and intangible assets	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromDisposalsOfPropertyPlantAndEquipmentIntangibleAssetsOtherThanGoodwillInvestmentPropertyAndOtherNoncurrentAssets
134	Gain on repurchase of debt securities	Concept (Monetary)	For Period	Credit	SID:AdjustmentsForGainsLossesOnRepurchaseOfDebtSecurities
135	Provision (Reversal) for consumption and services	Concept (Monetary)	For Period	Debit	SID:ProvisionReversalForConsumptionAndServices
136	Provision for actuarial liabilities	Concept (Monetary)	For Period	Debit	SID:AdjustmentsForProvisionsForActuarialLiabilities
137	PIS and COFINS credits	Concept (Monetary)	For Period	Credit	ifrs-full:GainLossThatRelatesToIdentifiableAssetsAcquiredOrLiabilitiesAssumedInBusinessCombination
138	Gain on business combination	Concept (Monetary)	For Period	Credit	SID:GainOnBusinessCombination
139	Net gain on sale of a foreign subsidiary	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromDisposalOrMaturityOfAvailableforsaleFinancialAssets
140	Gain on disposal of available for sale	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForLossesGainsOnDisposalOfNoncurrentAssets
141	Provision for environmental liabilities and decommissioning of assets	Concept (Monetary)	For Period	Debit	SID:AdjustmentsForProvisionsForEnvironmentalLiabilitiesAndDecommissioningOfAssets
142	Impairment of Transnordestina	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForImpairmentLossReversalOfImpairmentLossRecognisedInProfitOrLossPropertyPlantAndEquipment
143	Updated shares - Fair value through profit or loss (VJR)	Concept (Monetary)	For Period	Debit	SID:UpdatedSharesVJR
144	Other provisions	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseInExistingProvisionsOtherProvisions
145	Total	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForReconcileProfitLoss
146	Changes in assets and liabilities	Abstract			SID:AdjustmentsForChangesInAssetsAndLiabilitiesAbstract
147	Trade receivables - third parties	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDecreaseIncreaseInTradeAccountReceivable
148	Trade receivables - related parties	Concept (Monetary)	For Period	Debit	SID:AdjustmentsForDecreaseIncreaseInRelatedPartyTradeAccountReceivable
149	Inventories	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDecreaseIncreaseInInventories
150	Receivables from related parties/Dividends	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDecreaseIncreaseInOtherOperatingReceivables
151	Recoverable taxes	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxesRefundClassifiedAsOperatingActivities
152	Judicial deposits	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncreaseDecreaseInDepositsFromBanks
153	Trade payables	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncreaseDecreaseInTradeAccountPayable
154	Payroll and related taxes	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncreaseDecreaseInEmployeeBenefitLiabilities
155	Taxes in installments - REFIS	Concept (Monetary)	For Period	Debit	SID:AdjustmentsForIncreaseDecreaseInTaxesInInstallmentsRefis
156	Payables to related parties	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncreaseDecreaseInOtherOperatingPayables
157	Interest paid	Concept (Monetary)	For Period	Credit	ifrs-full:InterestPaidClassifiedAsOperatingActivities
158	Interest received	Concept (Monetary)	For Period	Debit	ifrs-full:InterestReceivedClassifiedAsOperatingActivities
159	Interest on swaps paid	Concept (Monetary)	For Period	Credit	SID:InterestOnSwapsPaidClassifiedAsOperatingActivities
160	Other	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDecreaseIncreaseInOtherAssets
161	Increase (Decrease) in assets and liabilities	Concept (Monetary)	For Period	Debit	SID:AdjustmentsForIncreaseDecreaseInAssetsAndLiabilities
162	Net cash generated by operating activities	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperatingActivities
163	Investments / acquisition of shares	Concept (Monetary)	For Period	Credit	ifrs-full:OtherCashPaymentsToAcquireEquityOrDebtInstrumentsOfOtherEntitiesClassifiedAsInvestingActivities
164	Purchase of property, plant and equipment	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfPropertyPlantAndEquipmentClassifiedAsInvestingActivities
165	Receipt/(Payment) in derivative transactions	Concept (Monetary)	For Period	Credit	SID:CashPaymentsForDerivativeTransactions
166	Purchase of intangible assets	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfIntangibleAssetsClassifiedAsInvestingActivities
167	Loans granted to related parties	Concept (Monetary)	For Period	Credit	ifrs-full:CashAdvancesAndLoansMadeToRelatedParties
168	Financial investment, net of redeemed amount	Concept (Monetary)	For Period	Debit	ifrs-full:OtherInflowsOutflowsOfCashClassifiedAsInvestingActivities
169	Loans received from related parties	Concept (Monetary)	For Period	Debit	ifrs-full:CashReceiptsFromRepaymentOfAdvancesAndLoansMadeToRelatedParties
170	Cash received by disposal of Usiminas' shares	Concept (Monetary)	For Period	Debit	SID:CashReceiptsFromDiscontinuedOperations
171	Cash and cash equivalents from discontinued operations	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInCashAndCashEquivalentsDiscontinuedOperations
172	Net cash received from the sale of a foreign subsidiary	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromChangesInOwnershipInterestsInSubsidiaries
173	Cash and cash equivalents on acquisition of control	Concept (Monetary)	For Period	Debit	SID:CashReceiptsFromAcquisitionOfControl
174	Net cash used in investing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInInvestingActivities
175	Borrowings and financing raised	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromBorrowingsClassifiedAsFinancingActivities
176	Cost of borrowing	Concept (Monetary)	For Period		ifrs-full:BorrowingCostsIncurred
177	Payment of borrowings	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfBorrowingsClassifiedAsFinancingActivities
178	Payment of dividends and interests on shareholder's equity	Concept (Monetary)	For Period	Credit	ifrs-full:DividendsPaidClassifiedAsFinancingActivities
179	Treasury shares	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromSaleOrIssueOfTreasuryShares
180	Forfaiting funding / drawee risk	Concept (Monetary)	For Period	Debit	SID:ProceedsFromForfaitingTransactions
181	Forfaiting amortization / drawee risk	Concept (Monetary)	For Period	Credit	SID:ForfaitingAmortization
182	Buyback of debt securities	Concept (Monetary)	For Period	Debit	ifrs-full:OtherInflowsOutflowsOfCashClassifiedAsFinancingActivities
183	Net cash used in financing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInFinancingActivities
184	Exchange rate changes on cash and cash equivalents of foreign subsidiaries	Concept (Monetary)	For Period	Debit	ifrs-full:EffectOfExchangeRateChangesOnCashAndCashEquivalents
185	Increase (Decrease) in cash and cash equivalents	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInCashAndCashEquivalents
186	Cash and cash equivalents at the beginning of the year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
187	Cash and cash equivalents at the end of the year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
188	00000006 - Statement - Consolidated Statement of Changes in Shareholders' Equity (Consolidated)	Network	*	*	http://csn.com.br/role/StatementOfChangesInShareholdersEquityConsolidated
189	Statement of changes in equity [table]	Table	*	*	ifrs-full:StatementOfChangesInEquityTable
190	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
191	Equity [member]	Member			ifrs-full:EquityMember
192	Paid-in Capital	Member			ifrs-full:AdditionalPaidinCapitalMember
193	Capital Reserve [Member]	Member			ifrs-full:CapitalReserveMember
194	Earnings Reserve [Member]	Member			ifrs-full:MiscellaneousOtherReservesMember
195	Retained Earnings (Accumulated Losses) [Member]	Member			ifrs-full:RetainedEarningsMember
196	Other Comprehensive Income [Member]	Member			ifrs-full:AccumulatedOtherComprehensiveIncomeMember
197	Shareholders' Equity [Member]	Member			ifrs-full:EquityAttributableToOwnersOfParentMember
198	Non-Controlling Interests [Member]	Member			ifrs-full:NoncontrollingInterestsMember
199	Statement of changes in equity [line items]	LineItems			ifrs-full:StatementOfChangesInEquityLineItems
200	Beginning balance	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
201	Ajusted opening balances	Concept (Monetary)	For Period	Credit	SID:AjustedOpeningBalancesEquity
202	Capital transactions with shareholders	Concept (Monetary)	For Period	Credit	ifrs-full:IssueOfEquity
203	Sales of treasury shares	Concept (Monetary)	For Period	Debit	ifrs-full:PurchaseOfTreasuryShares
204	Dividends	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsPaidOrdinaryShares
205	Profit on disposal of shares	Concept (Monetary)	For Period	Credit	SID:ProfitOnDisposalOfShares
206	Total comprehensive income	Concept (Monetary)	For Period	Credit	SID:ComprehensiveIncomeLoss
207	Profit (loss) for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
208	Other comprehensive income	Concept (Monetary)	For Period	Credit	SID:OtherComprehensiveIncomeLoss
209	Cumulative translation adjustments for the period	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationNetOfTax
210	Actuarial gain/(loss) on defined benefit pension plan, net of taxes	Concept (Monetary)	For Period	Debit	SID:ActuarialGainsLossesNetDefinedBenefitLiabilityAsset
211	Gain/(Loss) on available-for-sale assets, net of taxes	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnAvailableforsaleFinancialAssets
212	Gain/(loss) on percentage change in investments	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnChangeInValueOfTimeValueOfOptionsNetOfTax
213	Gain/(loss) on cash flow hedge accounting, net of taxes	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnHedgingInstrument
214	Gain/(loss) on hedge of net investments in foreign subsidiaries	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnHedgesOfNetInvestmentsInForeignOperationsNetOfTax
215	Gain/(loss) on business combination	Concept (Monetary)	For Period	Credit	SID:GainLossOnBusinessCombination
216	Internal changes in shareholders' equity	Concept (Monetary)	For Period	Credit	ifrs-full:ChangesInEquity
217	Constitution of reserves	Concept (Monetary)	For Period	Credit	SID:IncreaseDecreaseThroughTransferToMiscellaneousOtherReserves
218	Non-controlling interests in subsidiaries	Concept (Monetary)	For Period	Credit	SID:NoncontrollingInterestsInSubsidiaries
219	Ending balance	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
220	00000007 - Disclosure - 1. DESCRIPTION OF BUSINESS	Network	*	*	http://csn.com.br/role/DescriptionOfBusiness
221	Implied Table	Table	*	*	implied:Table
222	Description Of Business	Abstract			SID:DescriptionOfBusinessAbstract
223	DESCRIPTION OF BUSINESS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfGeneralInformationAboutFinancialStatementsExplanatory
224	00000008 - Disclosure - 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	Network	*	*	http://csn.com.br/role/SummaryOfSignificantAccountingPolicies
225	Implied Table	Table	*	*	implied:Table
226	Summary Of Significant Accounting Policies	Abstract			SID:SummaryOfSignificantAccountingPoliciesAbstract
227	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory
228	00000009 - Disclosure - 3. SALE OF FOREIGN SUBSIDIARY	Network	*	*	http://csn.com.br/role/SaleOfForeignSubsidiary
229	Implied Table	Table	*	*	implied:Table
230	Sale Of Foreign Subsidiary	Abstract			SID:SaleOfForeignSubsidiaryAbstract
231	SALE OF FOREIGN SUBSIDIARY	Concept (Text Block (HTML))	For Period		SID:DisclosureOfSaleOfForeignSubsidiaryExplanatory
232	00000010 - Disclosure - 4. CASH AND CASH EQUIVALENTS	Network	*	*	http://csn.com.br/role/CashAndCashEquivalents
233	Implied Table	Table	*	*	implied:Table
234	Cash and cash equivalents [abstract]	Abstract			ifrs-full:CashAndCashEquivalentsAbstract
235	CASH AND CASH EQUIVALENTS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCashAndCashEquivalentsExplanatory
236	00000011 - Disclosure - 5. FINANCIAL INVESTMENTS	Network	*	*	http://csn.com.br/role/FinancialInvestments
237	Implied Table	Table	*	*	implied:Table
238	Financial Investments	Abstract			SID:FinancialInvestmentsAbstract
239	FINANCIAL INVESTMENTS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInvestmentsOtherThanInvestmentsAccountedForUsingEquityMethodExplanatory
240	00000012 - Disclosure - 6. TRADE RECEIVABLES	Network	*	*	http://csn.com.br/role/TradeReceivables
241	Implied Table	Table	*	*	implied:Table
242	Trade Receivables	Abstract			SID:TradeReceivablesAbstract
243	TRADE RECEIVABLES	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTradeAndOtherReceivablesExplanatory
244	00000013 - Disclosure - 7. INVENTORIES	Network	*	*	http://csn.com.br/role/Inventories
245	Implied Table	Table	*	*	implied:Table
246	Inventories	Abstract			SID:InventoriesAbstract
247	INVENTORIES	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInventoriesExplanatory
248	00000014 - Disclosure - 8. OTHER CURRENT AND NON-CURRENT ASSETS	Network	*	*	http://csn.com.br/role/OtherCurrentAndNon-currentAssets
249	Implied Table	Table	*	*	implied:Table
250	Other Current And Non-current Assets	Abstract			SID:OtherCurrentAndNoncurrentAssetsAbstract
251	OTHER CURRENT AND NON-CURRENT ASSETS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOtherAssetsExplanatory
252	00000015 - Disclosure - 9. INVESTMENTS	Network	*	*	http://csn.com.br/role/Investments
253	Implied Table	Table	*	*	implied:Table
254	Investments	Abstract			SID:InvestmentAbstract
255	INVESTMENTS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInvestmentsAccountedForUsingEquityMethodExplanatory
256	00000016 - Disclosure - 10. PROPERTY, PLANT AND EQUIPMENT	Network	*	*	http://csn.com.br/role/PropertyPlantAndEquipment
257	Implied Table	Table	*	*	implied:Table
258	Property, plant and equipment [abstract]	Abstract			ifrs-full:PropertyPlantAndEquipmentAbstract
259	PROPERTY, PLANT AND EQUIPMENT	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfPropertyPlantAndEquipmentExplanatory
260	00000017 - Disclosure - 11. INTANGIBLE ASSETS	Network	*	*	http://csn.com.br/role/IntangibleAssets
261	Implied Table	Table	*	*	implied:Table
262	Intangible Assets	Abstract			SID:IntangibleAssetsAbstract
263	INTANGIBLE ASSETS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfIntangibleAssetsExplanatory
264	00000018 - Disclosure - 12. BORROWINGS, FINANCING AND DEBENTURES	Network	*	*	http://csn.com.br/role/BorrowingsFinancingAndDebentures
265	Implied Table	Table	*	*	implied:Table
266	Borrowings Financing And Debentures	Abstract			SID:BorrowingsFinancingAndDebenturesAbstract
267	BORROWINGS, FINANCING AND DEBENTURES	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfBorrowingsExplanatory
268	00000019 - Disclosure - 13. FINANCIAL INSTRUMENTS	Network	*	*	http://csn.com.br/role/FinancialInstruments
269	Implied Table	Table	*	*	implied:Table
270	Financial Instruments	Abstract			SID:FinancialInstrumentsAbstract
271	FINANCIAL INSTRUMENTS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialInstrumentsExplanatory
272	00000020 - Disclosure - 14. OTHER PAYABLES	Network	*	*	http://csn.com.br/role/OtherPayables
273	Implied Table	Table	*	*	implied:Table
274	Other Payables	Abstract			SID:OtherPayablesAbstract
275	OTHER PAYABLES	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTradeAndOtherPayablesExplanatory
276	00000021 - Disclosure - 15. INCOME TAX AND SOCIAL CONTRIBUTION	Network	*	*	http://csn.com.br/role/IncomeTaxAndSocialContribution
277	Implied Table	Table	*	*	implied:Table
278	Income Tax And Social Contribution	Abstract			SID:IncomeTaxAndSocialContributionAbstract
279	INCOME TAX AND SOCIAL CONTRIBUTION	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfIncomeTaxExplanatory
280	00000022 - Disclosure - 16. TAX INSTALLMENTS PROGRAMS	Network	*	*	http://csn.com.br/role/TaxInstallmentsPrograms
281	Implied Table	Table	*	*	implied:Table
282	Tax Installments Programs	Abstract			SID:TaxInstallmentsProgramsAbstract
283	TAX INSTALLMENTS PROGRAMS	Concept (Text Block (HTML))	For Period		SID:DisclosureOfIncomeTaxInstallmentsProgramsExplanatory
284	00000023 - Disclosure - 17. PROVISION FOR TAX, SOCIAL SECURITY, LABOR, CIVIL AND ENVIRONMENTAL RISKS AND JUDICIAL DEPOSITS	Network	*	*	http://csn.com.br/role/ProvisionForTaxSocialSecurityLaborCivilAndEnvironmentalRisksAndJudicialDeposits
285	Implied Table	Table	*	*	implied:Table
286	Provision For Tax Social Security Labor Civil And Environmental Risks And Judicial Deposits	Abstract			SID:ProvisionForTaxSocialSecurityLaborCivilAndEnvironmentalRisksAndJudicialDepositsAbstract
287	PROVISION FOR TAX, SOCIAL SECURITY, LABOR, CIVIL AND ENVIRONMENTAL RISKS AND JUDICIAL DEPOSITS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfProvisionsExplanatory
288	00000024 - Disclosure - 18. PROVISION FOR ENVIRONMENTAL LIABILITIES AND ASSET RETIREMENT OBLIGATIONS	Network	*	*	http://csn.com.br/role/ProvisionForEnvironmentalLiabilitiesAndAssetRetirementObligations
289	Implied Table	Table	*	*	implied:Table
290	Provision For Environmental Liabilities And Asset Retirement Obligations	Abstract			SID:ProvisionForEnvironmentalLiabilitiesAndAssetRetirementObligationsAbstract
291	PROVISION FOR ENVIRONMENTAL LIABILITIES AND ASSET RETIREMENT OBLIGATIONS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOtherProvisionsExplanatory
292	00000025 - Disclosure - 19. RELATED-PARTY BALANCES AND TRANSACTIONS	Network	*	*	http://csn.com.br/role/Related-partyBalancesAndTransactions
293	Implied Table	Table	*	*	implied:Table
294	Related-party Balances And Transactions	Abstract			SID:RelatedpartyBalancesAndTransactionsAbstract
295	RELATED-PARTY BALANCES AND TRANSACTIONS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesExplanatory
296	00000026 - Disclosure - 20. SHAREHOLDERS' EQUITY	Network	*	*	http://csn.com.br/role/ShareholdersEquity
297	Implied Table	Table	*	*	implied:Table
298	Shareholders Equity	Abstract			SID:ShareholdersEquityAbstract
299	SHAREHOLDERS' EQUITY	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfShareCapitalReservesAndOtherEquityInterestExplanatory
300	00000027 - Disclosure - 21. PAYMENT TO SHAREHOLDERS	Network	*	*	http://csn.com.br/role/PaymentToShareholders
301	Implied Table	Table	*	*	implied:Table
302	Payment To Shareholders	Abstract			SID:PaymentToShareholdersAbstract
303	PAYMENT TO SHAREHOLDERS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDividendsExplanatory
304	00000028 - Disclosure - 22. NET SALES AND SERVICES REVENUE	Network	*	*	http://csn.com.br/role/NetSalesAndServicesRevenue
305	Implied Table	Table	*	*	implied:Table
306	Net Sales And Services Revenue	Abstract			SID:NetSalesAndServicesRevenueAbstract
307	NET SALES AND SERVICES REVENUE	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfRevenueExplanatory
308	00000029 - Disclosure - 23. EXPENSES BY NATURE	Network	*	*	http://csn.com.br/role/ExpensesByNature
309	Implied Table	Table	*	*	implied:Table
310	Expenses By Nature	Abstract			SID:ExpensesByNatureAbstract
311	EXPENSES BY NATURE	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfExpensesByNatureExplanatory
312	00000030 - Disclosure - 24. OTHER OPERATING INCOME (EXPENSES)	Network	*	*	http://csn.com.br/role/OtherOperatingIncomeExpenses
313	Implied Table	Table	*	*	implied:Table
314	Other Operating Income	Abstract			SID:OtherOperatingIncomeExpensesAbstract
315	OTHER OPERATING INCOME (EXPENSES)	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOtherOperatingIncomeExpenseExplanatory
316	00000031 - Disclosure - 25. FINANCIAL INCOME (EXPENSES)	Network	*	*	http://csn.com.br/role/FinancialIncomeExpenses
317	Implied Table	Table	*	*	implied:Table
318	Financial Income	Abstract			SID:FinancialIncomeExpensesAbstract
319	FINANCIAL INCOME (EXPENSES)	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinanceIncomeExpenseExplanatory
320	00000032 - Disclosure - 26. SEGMENT INFORMATION	Network	*	*	http://csn.com.br/role/SegmentInformation
321	Implied Table	Table	*	*	implied:Table
322	Segment Information	Abstract			SID:SegmentInformationAbstract
323	SEGMENT INFORMATION	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOperatingSegmentsExplanatory
324	00000033 - Disclosure - 27. EMPLOYEE BENEFITS	Network	*	*	http://csn.com.br/role/EmployeeBenefits
325	Implied Table	Table	*	*	implied:Table
326	Employee Benefits	Abstract			SID:EmployeeBenefitsAbstract
327	EMPLOYEE BENEFITS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEmployeeBenefitsExplanatory
328	00000034 - Disclosure - 28. COMMITMENTS	Network	*	*	http://csn.com.br/role/Commitments
329	Implied Table	Table	*	*	implied:Table
330	Commitments	Abstract			SID:CommitmentsAbstract
331	COMMITMENTS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCommitmentsExplanatory
332	00000035 - Disclosure - 29. INSURANCE	Network	*	*	http://csn.com.br/role/Insurance
333	Implied Table	Table	*	*	implied:Table
334	Insurance	Abstract			SID:InsuranceDisclosureAbstract
335	INSURANCE	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInsuranceContractsExplanatory
336	00000036 - Disclosure - 30. ADDITIONAL INFORMATION TO CASH FLOWS	Network	*	*	http://csn.com.br/role/AdditionalInformationToCashFlows
337	Implied Table	Table	*	*	implied:Table
338	Additional Information To Cash Flows	Abstract			SID:AdditionalInformationToCashFlowsAbstract
339	ADDITIONAL INFORMATION TO CASH FLOWS	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCashFlowStatementExplanatory
340	00000037 - Disclosure - 31. EVENTS AFTER THE REPORTING PERIOD	Network	*	*	http://csn.com.br/role/EventsAfterReportingPeriod
341	Implied Table	Table	*	*	implied:Table
342	Events After Reporting Period	Abstract			SID:EventsAfterReportingPeriodAbstract
343	EVENTS AFTER THE REPORTING PERIOD	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEventsAfterReportingPeriodExplanatory
344	00000038 - Disclosure - 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	Network	*	*	http://csn.com.br/role/SummaryOfSignificantAccountingPoliciesPolicies
345	Implied Table	Table	*	*	implied:Table
346	Summary Of Significant Accounting Policies	Abstract			SID:SummaryOfSignificantAccountingPoliciesPoliciesAbstract
347	Basis of preparation and declaration of conformity	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfBasisOfPreparationOfFinancialStatementsExplanatory
348	Consolidated financial statements	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfBasisOfConsolidationExplanatory
349	Foreign currencies	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForForeignCurrencyTranslationExplanatory
350	Cash and cash equivalents	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyToDetermineComponentsOfCashAndCashEquivalents
351	Trade receivables	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForTradeAndOtherReceivablesExplanatory
352	Inventories	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForMeasuringInventories
353	Investments	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForInvestmentInAssociatesAndJointVenturesExplanatory
354	Business combination	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForBusinessCombinationsExplanatory
355	Property, plant and equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForPropertyPlantAndEquipmentExplanatory
356	Intangible assets	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIntangibleAssetsAndGoodwillExplanatory
357	Impairment of non-financial assets	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForImpairmentOfNonfinancialAssetsExplanatory
358	Employee benefits	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForEmployeeBenefitsExplanatory
359	Provisions	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForProvisionsExplanatory
360	Concessions	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForServiceConcessionArrangementsExplanatory
361	Share capital	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIssuedCapitalExplanatory
362	Revenue recognition	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForRecognitionOfRevenue
363	Financial income and financial expenses	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForFinanceIncomeAndCostsExplanatory
364	Income tax and social contribution	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIncomeTaxExplanatory
365	Earnings/(Loss) per share	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForEarningsPerShareExplanatory
366	Environmental and restoration costs	Concept (Text Block (HTML))	For Period		SID:DescriptionOfAccountingPolicyForEnvironmentalAndRestorationCostsExplanatory
367	Research and development	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForResearchAndDevelopmentExpenseExplanatory
368	Financial instruments	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForFinancialInstrumentsExplanatory
369	Segment information	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForSegmentReportingExplanatory
370	Government grants	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForGovernmentGrants
371	Noncurrent assets held for sale and discontinued operations	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForNoncurrentAssetsOrDisposalGroupsClassifiedAsHeldForSaleAndDiscontinuedOperationsExplanatory
372	New standards and interpretations issued and not yet adopted	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfInitialApplicationOfStandardsOrInterpretations
373	00000039 - Disclosure - 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	Network	*	*	http://csn.com.br/role/SummaryOfSignificantAccountingPoliciesTables
374	Implied Table	Table	*	*	implied:Table
375	Summary Of Significant Accounting Policies	Abstract			SID:SummaryOfSignificantAccountingPoliciesTablesAbstract
376	Subsidiaries, joint ventures and joint operations	Concept (Text Block (HTML))	For Period		SID:SummaryOfSubsidiariesJointVenturesAndJointOperationsTableTextBlock
377	Exclusive funds	Concept (Text Block (HTML))	For Period		SID:SummaryOfExclusiveFundsTableTextBlock
378	Concessions	Concept (Text Block (HTML))	For Period		SID:SummaryOfConcessionsTableTextBlock
379	New standards and interpretations issued and not yet adopted	Concept (Text Block (HTML))	For Period		SID:SummaryOfNewStandardsAndInterpretationsIssuedAndNotYetAdoptedTableTextBlock
380	00000040 - Disclosure - 3. SALE OF FOREIGN SUBSIDIARY (Tables)	Network	*	*	http://csn.com.br/role/SaleOfForeignSubsidiaryTables
381	Implied Table	Table	*	*	implied:Table
382	Sale Of Foreign Subsidiary	Abstract			SID:SaleOfForeignSubsidiaryTablesAbstract
383	Sale of foreign subsidiary	Concept (Text Block (HTML))	For Period		SID:SummaryOfSaleOfForeignSubsidiaryTableTextBlock
384	Net investment, results and cash flows from the sale of the investment	Concept (Text Block (HTML))	For Period		SID:SummaryOfNetInvestmentResultsAndCashFlowsFromSaleOfInvestmentTableTextBlock
385	00000041 - Disclosure - 4. CASH AND CASH EQUIVALENTS (Tables)	Network	*	*	http://csn.com.br/role/CashAndCashEquivalentsTables
386	Implied Table	Table	*	*	implied:Table
387	Cash And Cash Equivalents	Abstract			SID:CashAndCashEquivalentsTablesAbstract
388	Cash and cash equivalents	Concept (Text Block (HTML))	For Period		SID:SummaryOfCashAndCashEquivalentsTableTextBlock
389	00000042 - Disclosure - 5. FINANCIAL INVESTMENTS (Tables)	Network	*	*	http://csn.com.br/role/FinancialInvestmentsTables
390	Implied Table	Table	*	*	implied:Table
391	Financial Investments	Abstract			SID:FinancialInvestmentsTablesAbstract
392	FINANCIAL INVESTMENTS	Concept (Text Block (HTML))	For Period		SID:DetailInformationOfInvestmentsOtherThanInvestmentsAccountedForUsingEquityMethodExplanatory
393	00000043 - Disclosure - 6. TRADE RECEIVABLES (Tables)	Network	*	*	http://csn.com.br/role/TradeReceivablesTables
394	Implied Table	Table	*	*	implied:Table
395	Trade Receivables	Abstract			SID:TradeReceivablesTablesAbstract
396	Trade receivables	Concept (Text Block (HTML))	For Period		SID:SummaryOfTradeReceivablesTableTextBlock
397	Gross trade receivables from third parties	Concept (Text Block (HTML))	For Period		SID:SummaryOfGrossTradeReceivablesFromThirdPartiesTableTextBlock
398	Changes in allowance for doubtful debts	Concept (Text Block (HTML))	For Period		SID:SummaryOfChangesInAllowanceForDoubtfulDebtsTableTextBlock
399	00000044 - Disclosure - 7. INVENTORIES (Tables)	Network	*	*	http://csn.com.br/role/InventoriesTables
400	Implied Table	Table	*	*	implied:Table
401	Inventories	Abstract			SID:InventoriesTablesAbstract
402	Inventory	Concept (Text Block (HTML))	For Period		SID:SummaryOfInventoryTableTextBlock
403	Changes in provision for inventory losses	Concept (Text Block (HTML))	For Period		SID:SummaryOfChangesInProvisionForInventoryLossesTableTextBlock
404	00000045 - Disclosure - 8. OTHER CURRENT AND NON-CURRENT ASSETS (Tables)	Network	*	*	http://csn.com.br/role/OtherCurrentAndNon-currentAssetsTables
405	Implied Table	Table	*	*	implied:Table
406	Other Current And Non-current Assets	Abstract			SID:OtherCurrentAndNoncurrentAssetsTablesAbstract
407	Other current and non-current assets	Concept (Text Block (HTML))	For Period		SID:SummaryOfOtherCurrentAndNoncurrentAssetsTableTextBlock
408	00000046 - Disclosure - 9. INVESTMENTS (Tables)	Network	*	*	http://csn.com.br/role/InvestmentsTables
409	Implied Table	Table	*	*	implied:Table
410	Investments	Abstract			SID:InvestmentsTablesAbstract
411	Sale of the Subsidiary - CGPAR	Concept (Text Block (HTML))	For Period		SID:SummaryOfSaleOfSubsidiaryTableTextBlock
412	Direct equity interests in subsidiaries, joint ventures, joint operations, associates and other investments	Concept (Text Block (HTML))	For Period		SID:SummaryOfDirectEquityInterestsInSubsidiariesJointVenturesJointOperationsAssociatesAndOtherInvestmentsTableTextBlock
413	Changes of investments balances in subsidiaries, joint ventures, joint operations, associates and other investments	Concept (Text Block (HTML))	For Period		SID:SummaryOfChangesOfInvestmentsBalancesInSubsidiariesJointVenturesJointOperationsAssociatesAndOtherInvestmentsTableTextBlock
414	Equity in results	Concept (Text Block (HTML))	For Period		SID:SummaryOfEquityInResultsTableTextBlock
415	Joint ventures and joint operations financial information	Concept (Text Block (HTML))	For Period		SID:SummaryOfJointVenturesAndJointOperationsFinancialInformationTableTextBlock
416	Assumptions for impairment test	Concept (Text Block (HTML))	For Period		SID:SummaryOfAssumptionsForInvestmentImpairmentTestTableTextBlock
417	00000047 - Disclosure - 10. PROPERTY, PLANT AND EQUIPMENT (Tables)	Network	*	*	http://csn.com.br/role/PropertyPlantAndEquipmentTables
418	Implied Table	Table	*	*	implied:Table
419	Property, plant and equipment [abstract]	Abstract			ifrs-full:PropertyPlantAndEquipmentAbstract
420	Property, plant and equipment	Concept (Text Block (HTML))	For Period		SID:SummaryOfPropertyPlantAndEquipmentTableTextBlock
421	Construction in progress	Concept (Text Block (HTML))	For Period		SID:SummaryOfConstructionInProgressTableTextBlock
422	Estimated useful lives	Concept (Text Block (HTML))	For Period		SID:SummaryOfEstimatedUsefulLivesTableTextBlock
423	Capitalize borrowing costs rates	Concept (Text Block (HTML))	For Period		SID:SummaryOfCapitalizeBorrowingCostsRatesTableTextBlock
424	00000048 - Disclosure - 11. INTANGIBLE ASSETS (Tables)	Network	*	*	http://csn.com.br/role/IntangibleAssetsTables
425	Implied Table	Table	*	*	implied:Table
426	Intangible Assets	Abstract			SID:IntangibleAssetsTablesAbstract
427	Intangible assets	Concept (Text Block (HTML))	For Period		SID:SummaryOfIntangibleAssetsTableTextBlock
428	Estimated useful lives	Concept (Text Block (HTML))	For Period		SID:SummaryOfEstimatedUsefulLivesOfIntangibleAssetsTableTextBlock
429	Cash generating units	Concept (Text Block (HTML))	For Period		SID:SummaryOfCashGeneratingUnitsTableTextBlock
430	Assumptions for impairment test	Concept (Text Block (HTML))	For Period		SID:SummaryOfAssumptionsForIntangibleAssetImpairmentTestTableTextBlock
431	00000049 - Disclosure - 12. BORROWINGS, FINANCING AND DEBENTURES (Tables)	Network	*	*	http://csn.com.br/role/BorrowingsFinancingAndDebenturesTables
432	Implied Table	Table	*	*	implied:Table
433	Borrowings Financing And Debentures	Abstract			SID:BorrowingsFinancingAndDebenturesTablesAbstract
434	Borrowings, financing and debentures	Concept (Text Block (HTML))	For Period		SID:SummaryOfBorrowingsFinancingAndDebenturesTableTextBlock
435	Average interest rate	Concept (Text Block (HTML))	For Period		SID:SummaryOfAverageInterestRateOnBorrowingsTableTextBlock
436	Maturities of borrowings, financing and debentures	Concept (Text Block (HTML))	For Period		SID:SummaryOfMaturitiesOfBorrowingsFinancingAndDebenturesTableTextBlock
437	New funding transactions and amortization	Concept (Text Block (HTML))	For Period		SID:SummaryOfNewFundingTransactionsAndAmortizationTableTextBlock
438	Group captures and amortized loans	Concept (Text Block (HTML))	For Period		SID:SummaryOfGroupCapturesAndAmortizedLoansTableTextBlock
439	Borrowings, financing and debentures amortization	Concept (Text Block (HTML))	For Period		SID:SummaryOfBorrowingsFinancingAndDebenturesAmortizationTableTextBlock
440	00000050 - Disclosure - 13. FINANCIAL INSTRUMENTS (Tables)	Network	*	*	http://csn.com.br/role/FinancialInstrumentsTables
441	Implied Table	Table	*	*	implied:Table
442	Financial Instruments	Abstract			SID:FinancialInstrumentsTablesAbstract
443	Financial instruments	Concept (Text Block (HTML))	For Period		SID:SummaryOfFinancialInstrumentsTableTextBlock
444	Financial instruments at fair value through profit or loss	Concept (Text Block (HTML))	For Period		SID:SummaryOfFinancialInstrumentsAtFairValueThroughProfitOrLossTableTextBlock
445	Investments in financial instruments classified as available-for-sale	Concept (Text Block (HTML))	For Period		SID:SummaryOfInvestmentsInFinancialInstrumentsClassifiedAsAvailableForSaleTableTextBlock
446	Foreign exchange exposure	Concept (Text Block (HTML))	For Period		SID:SummaryOfForeignExchangeExposureTableTextBlock
447	Derivative financial instruments	Concept (Text Block (HTML))	For Period		SID:SummaryOfDerivativeFinancialInstrumentsTableTextBlock
448	Dollar x Euro swap	Concept (Text Block (HTML))	For Period		SID:SummaryOfDollarEuroSwapTableTextBlock
449	Hedging instruments	Concept (Text Block (HTML))	For Period		SID:SummaryOfHedgingInstrumentsTableTextBlock
450	Changes in hedge accounting	Concept (Text Block (HTML))	For Period		SID:SummaryOfChangesInHedgeAccountingTableTextBlock
451	Non-derivative financial liabilities	Concept (Text Block (HTML))	For Period		SID:SummaryOfNonDerivativeFinancialLiabilitiesTableTextBlock
452	Changes in net investment hedge	Concept (Text Block (HTML))	For Period		SID:SummaryOfChangesInNetInvestmentHedgeTableTextBlock
453	Currencies used in sensitivity analysis	Concept (Text Block (HTML))	For Period		SID:SummaryOfCurrenciesUsedInSensitivityAnalysisTableTextBlock
454	Interests used in sensitivity analysis	Concept (Text Block (HTML))	For Period		SID:SummaryOfInterestsUsedInSensitivityAnalysisTableTextBlock
455	Sensitivity analysis effects on income statement	Concept (Text Block (HTML))	For Period		SID:SummaryOfSensitivityAnalysisEffectsOnIncomeStatementTableTextBlock
456	Sensitivity analysis of interest rate swaps	Concept (Text Block (HTML))	For Period		SID:SummaryOfSensitivityAnalysisOfInterestRateSwapsTableTextBlock
457	Sensitivity analysis of changes in interest rates	Concept (Text Block (HTML))	For Period		SID:SummaryOfSensitivityAnalysisOfChangesInInterestRatesTableTextBlock
458	Contractual maturities of financial liabilities	Concept (Text Block (HTML))	For Period		SID:SummaryOfContractualMaturitiesOfFinancialLiabilitiesTableTextBlock
459	00000051 - Disclosure - 14. OTHER PAYABLES (Tables)	Network	*	*	http://csn.com.br/role/OtherPayablesTables
460	Implied Table	Table	*	*	implied:Table
461	Other Payables	Abstract			SID:OtherPayablesTablesAbstract
462	Other payables	Concept (Text Block (HTML))	For Period		SID:SummaryOfOtherPayablesTableTextBlock
463	00000052 - Disclosure - 15. INCOME TAX AND SOCIAL CONTRIBUTION (Tables)	Network	*	*	http://csn.com.br/role/IncomeTaxAndSocialContributionTables
464	Implied Table	Table	*	*	implied:Table
465	Income Tax And Social Contribution	Abstract			SID:IncomeTaxAndSocialContributionTablesAbstract
466	Income tax and social contribution income (expense)	Concept (Text Block (HTML))	For Period		SID:SummaryOfIncomeTaxAndSocialContributionIncomeExpenseTableTextBlock
467	Reconciliation of income tax and social contribution income (expense)	Concept (Text Block (HTML))	For Period		SID:SummaryOfReconciliationOfIncomeTaxAndSocialContributionIncomeExpenseTableTextBlock
468	Deferred income tax and social contribution	Concept (Text Block (HTML))	For Period		SID:SummaryOfDeferredIncomeTaxAndSocialContributionTableTextBlock
469	Deferred tax assets on tax losses and temporary differences	Concept (Text Block (HTML))	For Period		SID:SummaryOfDeferredTaxAssetsOnTaxLossesAndTemporaryDifferencesTableTextBlock
470	Income tax and social contribution recognized in shareholders' equity	Concept (Text Block (HTML))	For Period		SID:DisclosureOfInventoriesIncomeTaxAndSocialContributionRecognizedInShareholdersEquityExplanatory
471	00000053 - Disclosure - 16. TAX INSTALLMENTS PROGRAMS (Tables)	Network	*	*	http://csn.com.br/role/TaxInstallmentsProgramsTables
472	Implied Table	Table	*	*	implied:Table
473	Tax Installments Programs	Abstract			SID:TaxInstallmentsProgramsTablesAbstract
474	Taxes in installments	Concept (Text Block (HTML))	For Period		SID:SummaryOfTaxesInInstallmentsTableTextBlock
475	00000054 - Disclosure - 17. PROVISION FOR TAX, SOCIAL SECURITY, LABOR, CIVIL AND ENVIRONMENTAL RISKS AND JUDICIAL DEPOSITS (Tables)	Network	*	*	http://csn.com.br/role/ProvisionForTaxSocialSecurityLaborCivilAndEnvironmentalRisksAndJudicialDepositsTables
476	Implied Table	Table	*	*	implied:Table
477	Provision For Tax Social Security Labor Civil And Environmental Risks And Judicial Deposits	Abstract			SID:ProvisionForTaxSocialSecurityLaborCivilAndEnvironmentalRisksAndJudicialDepositsTablesAbstract
478	Accrued amounts and judicial deposits	Concept (Text Block (HTML))	For Period		SID:SummaryOfAccruedAmountsAndJudicialDepositsTableTextBlock
479	Changes in the provision for tax, social security, labor, civil and environmental risks	Concept (Text Block (HTML))	For Period		SID:SummaryOfChangesInProvisionForTaxSocialSecurityLaborCivilAndEnvironmentalRisksTableTextBlock
480	Legal matters with possible risk of loss	Concept (Text Block (HTML))	For Period		SID:SummaryOfLegalMattersWithPossibleRiskOfLossTableTextBlock
481	00000055 - Disclosure - 18. PROVISION FOR ENVIRONMENTAL LIABILITIES AND ASSET RETIREMENT OBLIGATIONS (Tables)	Network	*	*	http://csn.com.br/role/ProvisionForEnvironmentalLiabilitiesAndAssetRetirementObligationsTables
482	Implied Table	Table	*	*	implied:Table
483	Provision For Environmental Liabilities And Asset Retirement Obligations	Abstract			SID:ProvisionForEnvironmentalLiabilitiesAndAssetRetirementObligationsTablesAbstract
484	Provision for environmental liabilities and asset retirement obligation	Concept (Text Block (HTML))	For Period		SID:SummaryOfProvisionForEnvironmentalLiabilitiesAndAssetRetirementObligationTableTextBlock
485	00000056 - Disclosure - 19. RELATED-PARTY BALANCES AND TRANSACTIONS (Tables)	Network	*	*	http://csn.com.br/role/Related-partyBalancesAndTransactionsTables
486	Implied Table	Table	*	*	implied:Table
487	Related-party Balances And Transactions	Abstract			SID:RelatedpartyBalancesAndTransactionsTablesAbstract
488	Proposed dividends	Concept (Text Block (HTML))	For Period		SID:SummaryOfProposedDividendsTableTextBlock
489	Transactions with subsidiaries, joint ventures, associates, exclusive funds and other related parties, by transaction - assets and liabilities	Concept (Text Block (HTML))	For Period		SID:SummaryOfTransactionsWithSubsidiariesJointVenturesAssociatesExclusiveFundsAndOtherRelatedPartiesByTransactionAssetsAndLiabilitiesTableTextBlock
490	Transactions with subsidiaries, joint ventures, associates, exclusive funds and other related parties, by transaction - statement of income	Concept (Text Block (HTML))	For Period		SID:SummaryOfTransactionsWithSubsidiariesJointVenturesAssociatesExclusiveFundsAndOtherRelatedPartiesByTransactionStatementOfIncomeTableTextBlock
491	Transactions with subsidiaries, joint ventures, associates, exclusive funds and other related parties, by company - assets and liabilities	Concept (Text Block (HTML))	For Period		SID:SummaryOfTransactionsWithSubsidiariesJointVenturesAssociatesExclusiveFundsAndOtherRelatedPartiesByCompanyAssetsAndLiabilitiesTableTextBlock
492	Transactions with subsidiaries, joint ventures, associates, exclusive funds and other related parties, by company - statement of income	Concept (Text Block (HTML))	For Period		SID:SummaryOfTransactionsWithSubsidiariesJointVenturesAssociatesExclusiveFundsAndOtherRelatedPartiesByCompanyStatementOfIncomeTableTextBlock
493	Key management personnel compensation	Concept (Text Block (HTML))	For Period		SID:SummaryOfKeyManagementPersonnelCompensationTableTextBlock
494	00000057 - Disclosure - 20. SHAREHOLDERS' EQUITY (Tables)	Network	*	*	http://csn.com.br/role/ShareholdersEquityTables
495	Implied Table	Table	*	*	implied:Table
496	Shareholders Equity	Abstract			SID:ShareholdersEquityTablesAbstract
497	Ownership structure	Concept (Text Block (HTML))	For Period		SID:SummaryOfOwnershipStructureTableTextBlock
498	Share buyback programs	Concept (Text Block (HTML))	For Period		SID:SummaryOfShareBuybackProgramsTableTextBlock
499	Position of treasury shares	Concept (Text Block (HTML))	For Period		SID:SummaryOfPositionOfTreasurySharesTableTextBlock
500	Basic earnings (loss) per share	Concept (Text Block (HTML))	For Period		SID:SummaryOfBasicEarningsLossPerShareTableTextBlock
501	00000058 - Disclosure - 21. PAYMENT TO SHAREHOLDERS (Tables)	Network	*	*	http://csn.com.br/role/PaymentToShareholdersTables
502	Implied Table	Table	*	*	implied:Table
503	Payment To Shareholders	Abstract			SID:PaymentToShareholdersTablesAbstract
504	Deliberate and paid dividends	Concept (Text Block (HTML))	For Period		SID:SummaryOfDeliberateAndPaidDividendsTableTextBlock
505	00000059 - Disclosure - 22. NET SALES AND SERVICES REVENUE (Tables)	Network	*	*	http://csn.com.br/role/NetSalesAndServicesRevenueTables
506	Implied Table	Table	*	*	implied:Table
507	Net Sales And Services Revenue	Abstract			SID:NetSalesAndServicesRevenueTablesAbstract
508	Net sales and services revenue	Concept (Text Block (HTML))	For Period		SID:SummaryOfNetSalesAndServicesRevenueTableTextBlock
509	00000060 - Disclosure - 23. EXPENSES BY NATURE (Tables)	Network	*	*	http://csn.com.br/role/ExpensesByNatureTables
510	Implied Table	Table	*	*	implied:Table
511	Expenses By Nature	Abstract			SID:ExpensesByNatureTablesAbstract
512	Expenses by nature	Concept (Text Block (HTML))	For Period		SID:SummaryOfExpensesByNatureTableTextBlock
513	Depreciation, amortization and depletion	Concept (Text Block (HTML))	For Period		SID:DisclosureOfDepreciationAmortizationAndDepletionExplanatory
514	00000061 - Disclosure - 24. OTHER OPERATING INCOME (EXPENSES) (Tables)	Network	*	*	http://csn.com.br/role/OtherOperatingIncomeExpensesTables
515	Implied Table	Table	*	*	implied:Table
516	Other Operating Income Expenses	Abstract			SID:OtherOperatingIncomeExpensesTablesAbstract
517	Other operating income (expenses)	Concept (Text Block (HTML))	For Period		SID:SummaryOfOtherOperatingIncomeExpensesTableTextBlock
518	00000062 - Disclosure - 25. FINANCIAL INCOME (EXPENSES) (Tables)	Network	*	*	http://csn.com.br/role/FinancialIncomeExpensesTables
519	Implied Table	Table	*	*	implied:Table
520	Financial Income Expenses	Abstract			SID:FinancialIncomeExpensesTablesAbstract
521	Financial income (expenses)	Concept (Text Block (HTML))	For Period		SID:SummaryOfFinancialIncomeExpensesTableTextBlock
522	00000063 - Disclosure - 26. SEGMENT INFORMATION (Tables)	Network	*	*	http://csn.com.br/role/SegmentInformationTables
523	Implied Table	Table	*	*	implied:Table
524	Segment Information	Abstract			SID:SegmentInformationTablesAbstract
525	Consolidated results	Concept (Text Block (HTML))	For Period		SID:SummaryOfConsolidatedSegmentResultsTableTextBlock
526	EBITDA and Adjusted EBITDA	Concept (Text Block (HTML))	For Period		SID:SummaryOfSegmentEbitdaAndAdjustedEbitdaTableTextBlock
527	00000064 - Disclosure - 27. EMPLOYEE BENEFITS (Tables)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsTables
528	Implied Table	Table	*	*	implied:Table
529	Employee Benefits	Abstract			SID:EmployeeBenefitsTablesAbstract
530	Actuarial employee benefit assets and liabilities	Concept (Text Block (HTML))	For Period		SID:SummaryOfActuarialEmployeeBenefitAssetsAndLiabilitiesTableTextBlock
531	Reconciliation of employee benefits' assets and liabilities	Concept (Text Block (HTML))	For Period		SID:SummaryOfReconciliationOfEmployeeBenefitsAssetsAndLiabilitiesTableTextBlock
532	Changes in present value of the defined benefit obligation	Concept (Text Block (HTML))	For Period		SID:SummaryOfChangesInPresentValueOfDefinedBenefitObligationTableTextBlock
533	Changes in fair value of the plan assets	Concept (Text Block (HTML))	For Period		SID:SummaryOfChangesInFairValueOfPlanAssetsTableTextBlock
534	Employee benefits recognized in the income statement	Concept (Text Block (HTML))	For Period		SID:SummaryOfEmployeeBenefitsRecognizedInIncomeStatementTableTextBlock
535	Changes in actuarial gains and losses	Concept (Text Block (HTML))	For Period		SID:SummaryOfChangesInActuarialGainsAndLossesTableTextBlock
536	Breakdown of actuarial gains or losses	Concept (Text Block (HTML))	For Period		SID:SummaryOfBreakdownOfActuarialGainsOrLossesTableTextBlock
537	Actuarial assumptions used	Concept (Text Block (HTML))	For Period		SID:SummaryOfActuarialAssumptionsUsedTableTextBlock
538	Average life expectancy	Concept (Text Block (HTML))	For Period		SID:SummaryOfAverageLifeExpectancyTableTextBlock
539	Allocation of plan assets	Concept (Text Block (HTML))	For Period		SID:SummaryOfAllocationOfPlanAssetsTableTextBlock
540	Quantitative sensitivity analysis regarding the significant assumptions for the pension plans	Concept (Text Block (HTML))	For Period		SID:SummaryOfQuantitativeSensitivityAnalysisRegardingSignificantAssumptionsForPensionPlansTableTextBlock
541	Forecast benefit payments of the defined benefit plans	Concept (Text Block (HTML))	For Period		SID:SummaryOfForecastBenefitPaymentsOfDefinedBenefitPlansTableTextBlock
542	Post-employment health care plan amounts	Concept (Text Block (HTML))	For Period		SID:SummaryOfPostEmploymentHealthCarePlanAmountsTableTextBlock
543	Reconciliation of the healthcare liabilities	Concept (Text Block (HTML))	For Period		SID:SummaryOfReconciliationOfHealthcareLiabilitiesTableTextBlock
544	Actuarial gains and losses recognized in shareholders' equity	Concept (Text Block (HTML))	For Period		SID:SummaryOfActuarialGainsAndLossesRecognizedInShareholdersEquityTableTextBlock
545	Weighted average life expectancy	Concept (Text Block (HTML))	For Period		SID:SummaryOfWeightedAverageLifeExpectancyTableTextBlock
546	Actuarial assumptions used for calculating postemployment healthcare benefits	Concept (Text Block (HTML))	For Period		SID:SummaryOfActuarialAssumptionsUsedForCalculatingPostEmploymentHealthcareBenefitsTableTextBlock
547	Quantitative sensitivity analysis regarding the significant assumptions for the postemployment healthcare plans	Concept (Text Block (HTML))	For Period		SID:SummaryOfQuantitativeSensitivityAnalysisRegardingSignificantAssumptionsForPostEmploymentHealthcarePlansTableTextBlock
548	Forecast benefit payments of the postemployment healthcare plans	Concept (Text Block (HTML))	For Period		SID:SummaryOfForecastBenefitPaymentsOfPostEmploymentHealthcarePlansTableTextBlock
549	00000065 - Disclosure - 28. COMMITMENTS (Tables)	Network	*	*	http://csn.com.br/role/CommitmentsTables
550	Implied Table	Table	*	*	implied:Table
551	Commitments	Abstract			SID:CommitmentsTablesAbstract
552	Take-or-pay contracts	Concept (Text Block (HTML))	For Period		SID:SummaryOfTakeOrPayContractsTableTextBlock
553	Minimum future payments related to government concessions	Concept (Text Block (HTML))	For Period		SID:SummaryOfMinimumFuturePaymentsRelatedToGovernmentConcessionsTableTextBlock
554	00000066 - Disclosure - 30. ADDITIONAL INFORMATION TO CASH FLOWS (Tables)	Network	*	*	http://csn.com.br/role/AdditionalInformationToCashFlowsTables
555	Implied Table	Table	*	*	implied:Table
556	Additional Information To Cash Flows	Abstract			SID:AdditionalInformationToCashFlowsTablesAbstract
557	Additional information related to statement of cash flows	Concept (Text Block (HTML))	For Period		SID:SummaryOfAdditionalInformationRelatedToStatementOfCashFlowsTableTextBlock
558	00000069 - Disclosure - 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2)	Network	*	*	http://csn.com.br/role/SummaryOfSignificantAccountingPoliciesDetails2
559	Disclosure of detailed information about service concession arrangements [table]	Table	*	*	ifrs-full:DisclosureOfServiceConcessionArrangementsTable
560	Service concession arrangements [axis]	Axis			ifrs-full:ServiceConcessionArrangementsAxis
561	Service concession arrangements [member]	Member			ifrs-full:ServiceConcessionArrangementsMember
562	Concession 1	Member			SID:ServiceConcessionArrangements1Member
563	Concession 2	Member			SID:ServiceConcessionArrangements2Member
564	Concession 3	Member			SID:ServiceConcessionArrangements3Member
565	Concession 4	Member			SID:ServiceConcessionArrangements4Member
566	Concession 5	Member			SID:ServiceConcessionArrangements5Member
567	Disclosure of detailed information about service concession arrangements [line items]	LineItems			ifrs-full:DisclosureOfServiceConcessionArrangementsLineItems
568	Concession name	Concept (Text/String)	For Period		SID:NameOfServiceConcessionArrangement
569	Net book value	Concept (Monetary)	As Of	Debit	SID:ConcessionsNet
570	Classification in balance sheet	Concept (Text/String)	For Period		ifrs-full:DescriptionOfServiceConcessionArrangement
571	00000070 - Disclosure - 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 3)	Network	*	*	http://csn.com.br/role/SummaryOfSignificantAccountingPoliciesDetails3
572	Disclosure of expected impact of initial application of new standards or interpretations [table]	Table	*	*	ifrs-full:DescriptionOfExpectedImpactOfInitialApplicationOfNewStandardsOrInterpretationsTable
573	New IFRSs [axis]	Axis			ifrs-full:NewIFRSsAxis
574	New IFRSs [member]	Member			ifrs-full:NewIFRSsMember
575	Standard 1	Member			SID:NewIFRSs1Member
576	Standard 2	Member			SID:NewIFRSs2Member
577	Standard 3	Member			SID:NewIFRSs3Member
578	Disclosure of expected impact of initial application of new standards or interpretations [line items]	LineItems			ifrs-full:DescriptionOfExpectedImpactOfInitialApplicationOfNewStandardsOrInterpretationsLineItems
579	Standard	Concept (Text/String)	For Period		ifrs-full:TitleOfNewIFRS
580	Main items introduced by the standard	Concept (Text/String)	For Period		ifrs-full:DescriptionOfNatureOfImpendingChangeInAccountingPolicy
581	Effective date	Concept (Date)	For Period		ifrs-full:DateByWhichApplicationOfNewIFRSIsRequired
582	00000073 - Disclosure - 3. SALE OF FOREIGN SUBSIDIARY (Details 1)	Network	*	*	http://csn.com.br/role/SaleOfForeignSubsidiaryDetails1
583	SaleOfForeignSubsidiaryTable [Table]	Table	*	*	SID:SaleOfForeignSubsidiaryTable
584	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
585	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
586	LLC	Member			SID:LLCMember
587	SaleOfForeignSubsidiaryLineItems [Line Items]	LineItems			SID:SaleOfForeignSubsidiaryLineItems
588	ASSETS	Abstract			ifrs-full:AssetsAbstract
589	Current Assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssets
590	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
591	Trade Receivable	Concept (Monetary)	As Of	Debit	ifrs-full:TradeReceivables
592	Inventory	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
593	Other current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentAssets
594	Non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentAssets
595	Other non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentAssets
596	Property, plant and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
597	TOTAL ASSETS	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
598	LIABILITIES	Abstract			ifrs-full:LiabilitiesAbstract
599	Current Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLiabilities
600	Borrowings and Financing	Concept (Monetary)	As Of	Credit	SID:CurrentBorrowings
601	Social and Labor obligations	Concept (Monetary)	As Of	Credit	SID:SocialAndLaborObligations
602	Trade payables	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherPayables
603	Tax payables	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentTaxLiabilities
604	Other payables	Concept (Monetary)	As Of	Credit	ifrs-full:OtherPayables
605	Non-current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentLiabilities
606	Borrowings and Financing	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
607	Shareholders' equity (disposal)	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
608	TOTAL LIABILITIES	Concept (Monetary)	As Of	Credit	ifrs-full:Liabilities
609	00000074 - Disclosure - 3. SALE OF FOREIGN SUBSIDIARY (Details 2)	Network	*	*	http://csn.com.br/role/SaleOfForeignSubsidiaryDetails2
610	SaleOfForeignSubsidiaryTable [Table]	Table	*	*	SID:SaleOfForeignSubsidiaryTable
611	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
612	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
613	LLC	Member			SID:LLCMember
614	SaleOfForeignSubsidiaryLineItems [Line Items]	LineItems			SID:SaleOfForeignSubsidiaryLineItems
615	Net Revenues	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
616	Cost of sales and services	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
617	Gross profit	Concept (Monetary)	For Period	Credit	ifrs-full:GrossProfit
618	Selling expenses	Concept (Monetary)	For Period	Debit	ifrs-full:SalesAndMarketingExpense
619	General and administrative expenses	Concept (Monetary)	For Period	Debit	ifrs-full:AdministrativeExpense
620	Other operating expenses, net	Concept (Monetary)	For Period	Debit	ifrs-full:MiscellaneousOtherOperatingExpense
621	Profit before financial income (expenses) and taxes	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromOperatingActivities
622	Financial income (expenses), net	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncomeCost
623	Profit (loss) before taxes	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
624	Income tax and social contribution	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
625	Profit (loss) for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
626	00000075 - Disclosure - 3. SALE OF FOREIGN SUBSIDIARY (Details 3)	Network	*	*	http://csn.com.br/role/SaleOfForeignSubsidiaryDetails3
627	SaleOfForeignSubsidiaryTable [Table]	Table	*	*	SID:SaleOfForeignSubsidiaryTable
628	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
629	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
630	LLC	Member			SID:LLCMember
631	SaleOfForeignSubsidiaryLineItems [Line Items]	LineItems			SID:SaleOfForeignSubsidiaryLineItems
632	Net cash provided by (used) by operating activities	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperatingActivities
633	Net cash provided by (used) by investing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInInvestingActivities
634	Net cash provided by (used) by financing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInFinancingActivities
635	Increase (decrease) in cash and cash equivalents for the period	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInCashAndCashEquivalents
636	Cash and cash equivalents at the beginning of the year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
637	Cash and cash equivalents at the end of the year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
638	Net cash received from the sale of the asset	Concept (Monetary)	For Period	Debit	ifrs-full:OtherInflowsOutflowsOfCashClassifiedAsOperatingActivities
639	Cash and cash equivalents transferred on the sale of the assets	Concept (Monetary)	As Of	Credit	ifrs-full:CashTransferred
640	Working capital received	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseInWorkingCapital
641	Net cash provided by the sale of assets	Concept (Monetary)	For Period	Debit	SID:NetCashProvidedBySaleOfAssets
642	00000076 - Disclosure - 4. CASH AND CASH EQUIVALENTS (Details)	Network	*	*	http://csn.com.br/role/CashAndCashEquivalentsDetails
643	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
644	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
645	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
646	Brazil	Member			SID:BrazilMember
647	Abroad	Member			SID:AbroadMember
648	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
649	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
650	Government securities	Member			ifrs-full:DebtSecuritiesMember
651	Private securities	Member			ifrs-full:OtherEquitySecuritiesMember
652	Time deposits	Member			SID:TimeDepositsMember
653	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
654	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
655	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
656	Cash and banks	Concept (Monetary)	As Of	Debit	ifrs-full:BalancesWithBanks
657	Short-term investments	Concept (Monetary)	As Of	Debit	ifrs-full:ShorttermInvestmentsClassifiedAsCashEquivalents
658	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
659	00000077 - Disclosure - 5. FINANCIAL INVESTMENTS (Details)	Network	*	*	http://csn.com.br/role/FinancialInvestmentsDetails
660	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
661	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
662	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
663	CDB - Bank deposit certificate	Member			SID:BankDepositCertificateMember
664	Government securities	Member			ifrs-full:DebtSecuritiesMember
665	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
666	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
667	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
668	Financial Investments	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentInvestments
669	00000078 - Disclosure - 6. TRADE RECEIVABLES (Details)	Network	*	*	http://csn.com.br/role/TradeReceivablesDetails
670	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
671	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
672	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
673	Third parties	Member			SID:ThirdPartiesMember
674	Allowance for doubtful accounts	Member			SID:AllowanceForDoubtfulAccountMember
675	Subtotal	Member			SID:SubtotalMember
676	Related parties	Member			ifrs-full:RelatedPartiesMember
677	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
678	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
679	Domestic market	Member			SID:DomesticMarketMember
680	Foreign market	Member			SID:ForeignMarketMember
681	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
682	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
683	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
684	Trade receivables	Concept (Monetary)	As Of	Debit	ifrs-full:TradeReceivables
685	00000079 - Disclosure - 6. TRADE RECEIVABLES (Details 1)	Network	*	*	http://csn.com.br/role/TradeReceivablesDetails1
686	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
687	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
688	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
689	Third parties	Member			SID:ThirdPartiesMember
690	Range [Axis]	Axis			ifrs-full:RangeAxis
691	Ranges [member]	Member			ifrs-full:RangesMember
692	Current	Member			ifrs-full:CurrentMember
693	Past-due up to 30 days	Member			SID:PastDueUpTo30DaysMember
694	Past-due up to 180 days	Member			SID:PastDueUpTo180DaysMember
695	Past-due over 180 days	Member			SID:PastDueOver180DaysMember
696	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
697	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
698	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
699	Trade receivables	Concept (Monetary)	As Of	Debit	ifrs-full:TradeReceivables
700	00000080 - Disclosure - 6. TRADE RECEIVABLES (Details 2)	Network	*	*	http://csn.com.br/role/TradeReceivablesDetails2
701	Implied Table	Table	*	*	implied:Table
702	Trade Receivables	Abstract			SID:TradeReceivablesAbstract
703	Opening balance	Concept (Monetary)	As Of	Credit	ifrs-full:OtherProvisions
704	Expected credit losses	Concept (Monetary)	For Period	Credit	ifrs-full:ChangesInOtherProvisions
705	Recovery of receivables	Concept (Monetary)	For Period	Credit	ifrs-full:OtherReversalsOfProvisions
706	Closing balance	Concept (Monetary)	As Of	Credit	ifrs-full:OtherProvisions
707	00000081 - Disclosure - 6. TRADE RECEIVABLES (Details Narrative)	Network	*	*	http://csn.com.br/role/TradeReceivablesDetailsNarrative
708	Implied Table	Table	*	*	implied:Table
709	Trade Receivables	Abstract			SID:TradeReceivablesDetailsNarrativeAbstract
710	Trade receivables transaction costs	Concept (Monetary)	For Period	Debit	SID:TradeReceivablesTransactionCosts
711	00000082 - Disclosure - 7. INVENTORIES (Details)	Network	*	*	http://csn.com.br/role/InventoriesDetails
712	Implied Table	Table	*	*	implied:Table
713	Inventories	Abstract			SID:InventoriesDetailsAbstract
714	Finished goods	Concept (Monetary)	As Of	Debit	ifrs-full:FinishedGoods
715	Work in progress	Concept (Monetary)	As Of	Debit	ifrs-full:WorkInProgress
716	Raw materials	Concept (Monetary)	As Of	Debit	ifrs-full:RawMaterials
717	Spare parts	Concept (Monetary)	As Of	Debit	ifrs-full:SpareParts
718	Iron ore	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentOreStockpiles
719	Advances to suppliers	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAdvancesToSuppliers
720	(-) Provision for losses	Concept (Monetary)	As Of	Credit	ifrs-full:Provisions
721	Inventories	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
722	00000083 - Disclosure - 7. INVENTORIES (Details 1)	Network	*	*	http://csn.com.br/role/InventoriesDetails1
723	Implied Table	Table	*	*	implied:Table
724	Inventories	Abstract			SID:InventoriesDetails1Abstract
725	Provision for inventory losses, beginning	Concept (Monetary)	As Of	Credit	ifrs-full:Provisions
726	(Estimated losses) / Reversal of inventories with low turnover and obsolescence	Concept (Monetary)	For Period	Debit	ifrs-full:WritedownsReversalsOfInventories
727	Provision for inventory losses, ending	Concept (Monetary)	As Of	Credit	ifrs-full:Provisions
728	00000084 - Disclosure - 8. OTHER CURRENT AND NON-CURRENT ASSETS (Details)	Network	*	*	http://csn.com.br/role/OtherCurrentAndNon-currentAssetsDetails
729	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
730	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
731	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
732	Judicial deposits	Member			SID:JudicialDepositsMember
733	Credits with the PGFN	Member			SID:CreditsWithThePGFNMember
734	Recoverable taxes	Member			SID:RecoverableTaxesMember
735	Prepaid expenses	Member			SID:PrepaidExpensesMember
736	Actuarial asset - related party	Member			SID:ActuarialAssetRelatedPartyMember
737	Derivative financial instruments	Member			SID:DerivativeFinancialInstrumentsMember
738	Securities held for trading	Member			SID:SecuritiesHeldForTradingMember
739	Iron ore inventory	Member			SID:IronOreInventoryMember
740	Northeast Investment Fund - FINOR	Member			SID:NortheastInvestmentFundFINORMember
741	Other receivables	Member			SID:OtherReceivablesMember
742	Loans with related parties	Member			SID:LoansWithRelatedPartiesMember
743	Other receivables from related parties	Member			SID:OtherReceivablesFromRelatedPartiesMember
744	Monetary adjustment related to the Eletrobras's compulsory loan	Member			SID:MonetaryAdjustmentRelatedToTheEletrobrassCompulsoryLoanMember
745	Dividends receivable	Member			SID:DividendsReceivableMember
746	Debit of employees	Member			SID:DebitOfEmployeesMember
747	Other credits	Member			SID:OtherCreditsMember
748	Other	Member			SID:OtherMember
749	Sea freight	Member			SID:SeaFreightMember
750	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
751	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
752	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
753	Other current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentNonfinancialAssets
754	Other non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentNonfinancialAssets
755	00000085 - Disclosure - 9. INVESTMENTS (Details)	Network	*	*	http://csn.com.br/role/InvestmentsDetails
756	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
757	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
758	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
759	Joint Venture/Joint Operation 1	Member			SID:JointVenturesJointOperation1Member
760	Joint Venture/Joint Operation 2	Member			SID:JointVenturesJointOperation2Member
761	Joint Venture/Joint Operation 3	Member			SID:JointVenturesJointOperation3Member
762	Joint Venture/Joint Operation	Member			SID:JointVenturesJointOperationMember
763	Associate 1	Member			SID:Associates1Member
764	Associate	Member			ifrs-full:AssociatesMember
765	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
766	Joint venture and joint operation name	Concept (Text/String)	For Period		ifrs-full:NameOfJointVenture
767	Associate name	Concept (Text/String)	For Period		ifrs-full:NameOfAssociate
768	Number of common shares held by CSN	Concept (Shares)	As Of		ifrs-full:SharesInEntityHeldByEntityOrByItsSubsidiariesOrAssociates
769	Number of preferred shares held by CSN	Concept (Shares)	As Of		SID:PreferredSharesInEntityHeldByEntityOrByItsSubsidiariesOrAssociates
770	Direct equity interest, joint venture and joint operation	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInJointVenture
771	Direct equity interest, associate	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInAssociate
772	Assets	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
773	Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:Liabilities
774	Shareholders' equity	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
775	Fair Value Allocation	Concept (Monetary)	For Period	Credit	SID:FairValueAllocation
776	Profit (loss) for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
777	Classified as available for sale	Abstract			SID:ClassifiedAsAvailableForSaleAbstract
778	Usiminas	Concept (Monetary)	As Of	Debit	SID:Usiminas
779	Panatlantica	Concept (Monetary)	As Of	Debit	SID:Panatlantica
780	Classified as available for sale	Concept (Monetary)	As Of	Debit	ifrs-full:FinancialAssetsAvailableforsale
781	Others investments	Abstract			SID:OthersInvestmentsAbstract
782	Others investments	Concept (Monetary)	As Of	Debit	SID:TotalOtherInvestments
783	Total Investments	Concept (Monetary)	As Of	Debit	SID:TotalInvestments
784	00000086 - Disclosure - 9. INVESTMENTS (Details 1)	Network	*	*	http://csn.com.br/role/InvestmentsDetails1
785	Implied Table	Table	*	*	implied:Table
786	Investments	Abstract			SID:InvestmentsDetails1Abstract
787	Investments in associates and joint controlled entities, beginning	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentsInSubsidiariesJointVenturesAndAssociates
788	Capital increase	Concept (Monetary)	For Period	Debit	SID:CapitalIncreaseAcquisitionOfShares
789	Dividends	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsReceivedFromInvestmentsAccountedForUsingEquityMethodClassifiedAsInvestingActivities
790	Comprehensive income (1)	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeBeforeTaxGainsLossesFromInvestmentsInEquityInstruments
791	Equity in results of affiliated companies (2)	Concept (Monetary)	For Period	Debit	SID:EquityPickup
792	Received from sale of Usimina's shares	Concept (Monetary)	For Period	Debit	SID:ReceiptOfSaleOfSharesUsiminas
793	Update of shares measured at Fair Value through profit or loss (VJR) (note 13 II)	Concept (Monetary)	For Period	Debit	SID:UpdateOfVJRShares
794	Amortization of fair value - investment in MRS	Concept (Monetary)	For Period	Credit	SID:AmortizationOfFairValueInvestmentInMrs
795	Others	Concept (Monetary)	For Period	Credit	SID:OtherAdjustmentsToInvestmentsInSubsidiariesJointVenturesAndAssociates
796	Investments in associates and joint controlled entities, ending	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentsInSubsidiariesJointVenturesAndAssociates
797	00000087 - Disclosure - 9. INVESTMENTS (Details 2)	Network	*	*	http://csn.com.br/role/InvestmentsDetails2
798	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
799	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
800	Entity [Domain]	Member			dei:EntityDomain
801	MRS Logistica S.A.	Member			SID:MRSLogisticaSAMember
802	CBSI - Companhia Brasileira de Servicos de Infraestrutura	Member			SID:CBSIMember
803	Transnordestina	Member			SID:TransnordestinaMember
804	Arvedi Metalfer do Brasil	Member			SID:ArvediMetalferDoBrasilMember
805	Others	Member			SID:OthersMember
806	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
807	Equity in results of affiliated companies	Concept (Monetary)	For Period	Credit	SID:ShareOfProfitLossOfAssociatesAndJointVenturesAccountedForUsingEquityMethodGross
808	Eliminations	Abstract			SID:EliminationsAbstract
809	To cost of sales	Concept (Monetary)	For Period	Credit	SID:EliminationsToCostOfSalesFromSubsidiariesJointlyControlledEntitiesAndAssociates
810	To taxes	Concept (Monetary)	For Period	Credit	SID:EliminationsToTaxesFromSubsidiariesJointlyControlledEntitiesAndAssociates
811	Others	Abstract			SID:OthersAbstract
812	Amortization of fair value - investment in MRS	Concept (Monetary)	For Period	Credit	SID:AmortizationOfFairValueInvestmentInMrs
813	Others	Concept (Monetary)	For Period	Credit	SID:AmortizationOfFairValueInvestmentOthers
814	Equity in results adjusted	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfAssociatesAndJointVenturesAccountedForUsingEquityMethod
815	00000088 - Disclosure - 9. INVESTMENTS (Details 3)	Network	*	*	http://csn.com.br/role/InvestmentsDetails3
816	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
817	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
818	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
819	Joint Venture	Member			ifrs-full:JointVenturesMember
820	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
821	Entity [Domain]	Member			dei:EntityDomain
822	MRS Logistica	Member			SID:MRSLogisticaMember
823	CBSI	Member			SID:CBSI1Member
824	Transnordestina Logistica	Member			SID:TransnordestinaLogisticaMember
825	Ita Energetica	Member			SID:ItaEnergeticaMember
826	Joint operations [axis]	Axis			ifrs-full:JointOperationsAxis
827	Entity's total for joint operations [member]	Member			ifrs-full:EntitysTotalForJointOperationsMember
828	Joint Operation	Member			ifrs-full:JointOperationsMember
829	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
830	Current assets	Abstract			ifrs-full:CurrentAssetsAbstract
831	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
832	Advances to suppliers	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAdvancesToSuppliers
833	Other current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentAssets
834	Total current assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssets
835	Non-current assets	Abstract			ifrs-full:NoncurrentAssetsAbstract
836	Other non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentAssets
837	Investments, PP&E and intangible assets	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
838	Tota non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentAssets
839	Total assets	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
840	Current liabilities	Abstract			ifrs-full:CurrentLiabilitiesAbstract
841	Borrowings and financing	Concept (Monetary)	As Of	Credit	ifrs-full:ShorttermBorrowings
842	Other current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:OtherCurrentLiabilities
843	Total current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLiabilities
844	Non-current liabilities	Abstract			ifrs-full:NoncurrentLiabilitiesAbstract
845	Borrowings and financing	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
846	Other non-current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:OtherNoncurrentLiabilities
847	Total non-current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentLiabilities
848	Shareholders' equity	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
849	Total liabilities and shareholders' equity	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAndLiabilities
850	00000089 - Disclosure - 9. INVESTMENTS (Details 4)	Network	*	*	http://csn.com.br/role/InvestmentsDetails4
851	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
852	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
853	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
854	Joint Venture	Member			ifrs-full:JointVenturesMember
855	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
856	Entity [Domain]	Member			dei:EntityDomain
857	MRS Logistica	Member			SID:MRSLogisticaMember
858	CBSI	Member			SID:CBSI1Member
859	Transnordestina Logistica	Member			SID:TransnordestinaLogisticaMember
860	Ita Energetica	Member			SID:ItaEnergeticaMember
861	Joint operations [axis]	Axis			ifrs-full:JointOperationsAxis
862	Entity's total for joint operations [member]	Member			ifrs-full:EntitysTotalForJointOperationsMember
863	Joint Operation	Member			ifrs-full:JointOperationsMember
864	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
865	Net revenues	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
866	Cost of sales and services	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
867	Gross profit	Concept (Monetary)	For Period	Credit	ifrs-full:GrossProfit
868	Operating (expense) income	Concept (Monetary)	For Period	Credit	ifrs-full:OtherOperatingIncomeExpense
869	Finance income (costs), net	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncomeCost
870	Income before income tax and social contribution	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
871	Current and deferred income tax and social contribution	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
872	Profit (loss) for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
873	00000091 - Disclosure - 9. INVESTMENTS (Details Narrative)	Network	*	*	http://csn.com.br/role/InvestmentsDetailsNarrative
874	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
875	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
876	Entity [Domain]	Member			dei:EntityDomain
877	Consorcio da Usina Hidrelectrica de Igarapava	Member			SID:ConsorcioDaUsinaHidrelectricaDeIgarapavaMember
878	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
879	Property, plant and equipment	Concept (Monetary)	As Of	Debit	SID:PropertyPlantAndEquipments
880	Expenses	Concept (Monetary)	For Period		ifrs-full:DepreciationPropertyPlantAndEquipment
881	00000092 - Disclosure - 10. PROPERTY, PLANT AND EQUIPMENT (Details)	Network	*	*	http://csn.com.br/role/PropertyPlantAndEquipmentDetails
882	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
883	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
884	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
885	Land	Member			ifrs-full:LandMember
886	Buildings and Infrastructure	Member			ifrs-full:BuildingsMember
887	Machinery, equipment and facilities	Member			ifrs-full:MachineryMember
888	Furniture and fixtures	Member			ifrs-full:FixturesAndFittingsMember
889	Construction in progress	Member			ifrs-full:ConstructionInProgressMember
890	Other	Member			ifrs-full:OtherPropertyPlantAndEquipmentMember
891	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
892	Cost, beginning	Concept (Monetary)	As Of	Debit	SID:GrossPropertyPlantAndEquipment
893	Accumulated depreciation, beginning	Concept (Monetary)	As Of	Credit	SID:AccumulatedDepreciationPropertyPlantAndEquipment
894	Property, plant and equipment, beginning	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
895	Translation Adjustment	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesPropertyPlantAndEquipment
896	Acquisitions	Concept (Monetary)	For Period	Debit	SID:AdditionsToPropertyPlantAndEquipment
897	Capitalized interest	Concept (Monetary)	For Period	Credit	SID:PropertyPlantAndEquipmentCapitalizedInterest
898	Write-off and estimative losses, net of reversed	Concept (Monetary)	For Period	Credit	ifrs-full:DisposalsPropertyPlantAndEquipment
899	Depreciation	Concept (Monetary)	For Period		ifrs-full:DepreciationPropertyPlantAndEquipment
900	Transfers to other asset categories	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughTransfersAndOtherChangesPropertyPlantAndEquipment
901	Write-off - sale of subsidiary LLC	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughOtherChangesPropertyPlantAndEquipment
902	Transfers to intangible assets	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughTransfersAndOtherChangesIntangibleAssetsAndGoodwill
903	Acquisition control - CGPAR	Concept (Monetary)	For Period	Debit	ifrs-full:AcquisitionsThroughBusinessCombinationsPropertyPlantAndEquipment
904	Goodwill - Acquisition control CGPAR	Concept (Monetary)	For Period	Debit	ifrs-full:AdditionalRecognitionGoodwill
905	Transfers of metalic - Held for sale	Concept (Monetary)	For Period	Credit	ifrs-full:DecreaseThroughClassifiedAsHeldForSalePropertyPlantAndEquipment
906	Others	Concept (Monetary)	For Period	Debit	ifrs-full:ChangesInPropertyPlantAndEquipment
907	Property, plant and equipment, ending	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
908	Cost, ending	Concept (Monetary)	As Of	Debit	SID:GrossPropertyPlantAndEquipment
909	Accumulated depreciation, ending	Concept (Monetary)	As Of	Credit	SID:AccumulatedDepreciationPropertyPlantAndEquipment
910	00000094 - Disclosure - 10. PROPERTY, PLANT AND EQUIPMENT (Details 2)	Network	*	*	http://csn.com.br/role/PropertyPlantAndEquipmentDetails2
911	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
912	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
913	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
914	Buildings	Member			SID:Buildings1Member
915	Machinery, equipment and facilities	Member			ifrs-full:MachineryMember
916	Furniture and fixtures	Member			ifrs-full:FixturesAndFittingsMember
917	Other	Member			SID:OtherMember
918	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
919	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
920	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
921	Estimated useful life	Concept (Text/String)	For Period		ifrs-full:UsefulLivesOrDepreciationRatesPropertyPlantAndEquipment
922	00000095 - Disclosure - 10. PROPERTY, PLANT AND EQUIPMENT (Details 3)	Network	*	*	http://csn.com.br/role/PropertyPlantAndEquipmentDetails3
923	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
924	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
925	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
926	Unspecified projects	Member			SID:UnspecifiedProjectsMember
927	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
928	Capitalized borrowing costs rate (in percent)	Concept (Percent)	For Period		ifrs-full:CapitalisationRateOfBorrowingCostsEligibleForCapitalisation
929	00000096 - Disclosure - 10. PROPERTY, PLANT AND EQUIPMENT (Details Narrative)	Network	*	*	http://csn.com.br/role/PropertyPlantAndEquipmentDetailsNarrative
930	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
931	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
932	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
933	Unspecified projects	Member			SID:UnspecifiedProjectsMember
934	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
935	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
936	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
937	Capitalized borrowing costs	Concept (Monetary)	For Period		ifrs-full:BorrowingCostsCapitalised
938	00000097 - Disclosure - 11. INTANGIBLE ASSETS (Details)	Network	*	*	http://csn.com.br/role/IntangibleAssetsDetails
939	Disclosure of detailed information about intangible assets [table]	Table	*	*	ifrs-full:DisclosureOfIntangibleAssetsTable
940	Classes of intangible assets and goodwill [axis]	Axis			ifrs-full:ClassesOfIntangibleAssetsAndGoodwillAxis
941	Intangible assets and goodwill [member]	Member			ifrs-full:IntangibleAssetsAndGoodwillMember
942	Goodwill	Member			ifrs-full:GoodwillMember
943	Customer relationships	Member			ifrs-full:CustomerrelatedIntangibleAssetsMember
944	Software	Member			ifrs-full:ComputerSoftwareMember
945	Trademark and patents	Member			ifrs-full:BrandNamesMember
946	Rights and licenses	Member			SID:RightsAndLicencesMember
947	Others	Member			SID:OthersMember
948	Disclosure of detailed information about intangible assets [line items]	LineItems			ifrs-full:DisclosureOfIntangibleAssetsLineItems
949	Cost, beginning	Concept (Monetary)	As Of	Debit	SID:GrossIntangibleAssetsAndGoodwill
950	Accumulated amortization, beginning	Concept (Monetary)	As Of	Credit	SID:AccumulatedAmortizationIntangibleAssetsAndGoodwill
951	Adjustment for accumulated recoverable value, beginning	Concept (Monetary)	As Of	Credit	SID:AdjustmentForAccumulatedRecoverableValue
952	Intangible assets, beginning	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsAndGoodwill
953	Translation Adjustment	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesIntangibleAssetsAndGoodwill
954	Acquisitions and expenditures	Concept (Monetary)	For Period	Debit	ifrs-full:AdditionsOtherThanThroughBusinessCombinationsIntangibleAssetsOtherThanGoodwill
955	Transfer of property, plant and equipment	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughTransfersPropertyPlantAndEquipment
956	Write-offs/disposals	Concept (Monetary)	For Period	Credit	ifrs-full:DisposalsIntangibleAssetsAndGoodwill
957	Amortization	Concept (Monetary)	For Period		ifrs-full:AmortisationIntangibleAssetsOtherThanGoodwill
958	Aquisition control - CGPAR	Concept (Monetary)	For Period	Debit	ifrs-full:AcquisitionsThroughBusinessCombinationsIntangibleAssetsAndGoodwill
959	Transfer of Metalic - Held for sale	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughTransfersIntangibleAssetsAndGoodwill
960	Intangible assets, ending	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsAndGoodwill
961	Cost, ending	Concept (Monetary)	As Of	Debit	SID:GrossIntangibleAssetsAndGoodwill
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1234	Interest rate (in percent)	Concept (Percent)	As Of		SID:SensitivityAnalysisYearlyInterestRate
1235	Impact on profit or loss	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnIneffectivenessOfCashFlowHedgesRecognisedInProfitOrLoss
1236	00000122 - Disclosure - 13. FINANCIAL INSTRUMENTS (Details 14)	Network	*	*	http://csn.com.br/role/FinancialInstrumentsDetails14
1237	Disclosure of financial liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFinancialLiabilitiesTable
1238	Classes of financial liabilities [axis]	Axis			ifrs-full:ClassesOfFinancialLiabilitiesAxis
1239	Financial liabilities, class [member]	Member			ifrs-full:FinancialLiabilitiesMember
1240	Borrowings, financing and debentures	Member			SID:BorrowingsFinancingAndDebenturesMember
1241	Trade payables	Member			SID:TradePayablesMember
1242	Dividends and interest on capital	Member			SID:DividendsAndInterestOnCapitalMember
1243	Range [Axis]	Axis			ifrs-full:RangeAxis
1244	Ranges [member]	Member			ifrs-full:RangesMember
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1246	From one to two years	Member			ifrs-full:LaterThanOneYearAndNotLaterThanTwoYearsMember
1247	From two to five years	Member			ifrs-full:LaterThanTwoYearsAndNotLaterThanFiveYearsMember
1248	Over five years	Member			ifrs-full:LaterThanFiveYearsMember
1249	Disclosure of financial liabilities [line items]	LineItems			ifrs-full:DisclosureOfFinancialLiabilitiesLineItems
1250	Contractual maturities	Concept (Monetary)	As Of	Credit	SID:ContractualMaturities
1251	00000123 - Disclosure - 13. FINANCIAL INSTRUMENTS (Details 15)	Network	*	*	http://csn.com.br/role/FinancialInstrumentsDetails15
1252	Disclosure of financial liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFinancialLiabilitiesTable
1253	Classes of financial liabilities [axis]	Axis			ifrs-full:ClassesOfFinancialLiabilitiesAxis
1254	Financial liabilities, class [member]	Member			ifrs-full:FinancialLiabilitiesMember
1255	Perpetual bonds	Member			SID:PerpetualBondsMember
1256	Fixed rate notes	Member			SID:FixedRateNotesMember
1257	Disclosure of financial liabilities [line items]	LineItems			ifrs-full:DisclosureOfFinancialLiabilitiesLineItems
1258	Carrying amount	Concept (Monetary)	As Of	Credit	SID:LongtermBorrowingsCarryingAmount
1259	Fair value	Concept (Monetary)	As Of	Credit	ifrs-full:FinancialLiabilitiesAtFairValue
1260	00000124 - Disclosure - 13. FINANCIAL INSTRUMENTS (Details 16)	Network	*	*	http://csn.com.br/role/FinancialInstrumentsDetails16
1261	Implied Table	Table	*	*	implied:Table
1262	Financial Instruments	Abstract			SID:FinancialInstrumentsDetails16Abstract
1263	Shareholder's equity (equity)	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
1264	Borrowings and Financing (Third-party capital)	Concept (Monetary)	As Of	Credit	SID:BorrowingsAndFinancingThirdPartyCapital
1265	Gross Debit/Shareholder's equity	Concept (Pure)	As Of		SID:DebtEquityRatio
1266	00000125 - Disclosure - 13. FINANCIAL INSTRUMENTS (Details Narrative)	Network	*	*	http://csn.com.br/role/FinancialInstrumentsDetailsNarrative
1267	Implied Table	Table	*	*	implied:Table
1268	Financial Instruments	Abstract			SID:FinancialInstrumentsDetailsNarrativeAbstract
1269	Investments available for sale, net of taxes	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxAvailableforsaleFinancialAssets
1270	00000126 - Disclosure - 14. OTHER PAYABLES (Details)	Network	*	*	http://csn.com.br/role/OtherPayablesDetails
1271	Disclosure of fair value measurement of liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesTable
1272	Classes of liabilities [axis]	Axis			ifrs-full:ClassesOfLiabilitiesAxis
1273	Liabilities [member]	Member			ifrs-full:LiabilitiesMember
1274	Payables to related parties	Member			SID:PayablesToRelatedPartiesMember
1275	Derivative financial instruments	Member			SID:DerivativeFinancialInstrumentsMember
1276	Dividends and interest on capital payable	Member			SID:DividendsAndInterestOnCapitalPayableMember
1277	Advances from customers	Member			SID:AdvancesFromCustomersMember
1278	Taxes in installments	Member			SID:TaxesInInstallmentsMember
1279	Profit sharing - employees	Member			SID:ProfitSharingEmployeesMember
1280	Freight provision	Member			SID:FreightProvisionMember
1281	Provision for industrial restructuring	Member			SID:ProvisionForIndustrialRestructuringMember
1282	Taxes payable	Member			SID:TaxesPayableMember
1283	Other provision	Member			SID:OtherProvisionMember
1284	Third party materials in our possession	Member			SID:ThirdPartyMaterialsInOurPossessionMember
1285	Other payables	Member			SID:OtherPayablesMember
1286	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
1287	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
1288	Parent Company	Member			ifrs-full:ParentMember
1289	Disclosure of fair value measurement of liabilities [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesLineItems
1290	Other payables, current	Concept (Monetary)	As Of	Credit	ifrs-full:OtherCurrentPayables
1291	Other payables, noncurrent	Concept (Monetary)	As Of	Credit	ifrs-full:OtherNoncurrentPayables
1292	00000127 - Disclosure - 15. INCOME TAX AND SOCIAL CONTRIBUTION (Details)	Network	*	*	http://csn.com.br/role/IncomeTaxAndSocialContributionDetails
1293	Implied Table	Table	*	*	implied:Table
1294	Income Tax And Social Contribution	Abstract			SID:IncomeTaxAndSocialContributionDetailsAbstract
1295	Income tax and social contribution income (expense), current	Concept (Monetary)	For Period	Debit	ifrs-full:CurrentTaxExpenseIncome
1296	Income tax and social contribution income (expense), deferred	Concept (Monetary)	For Period	Debit	ifrs-full:DeferredTaxExpenseIncome
1297	Income tax and social contribution income (expense)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
1298	00000131 - Disclosure - 15. INCOME TAX AND SOCIAL CONTRIBUTION (Details 4)	Network	*	*	http://csn.com.br/role/IncomeTaxAndSocialContributionDetails4
1299	Implied Table	Table	*	*	implied:Table
1300	Income Tax And Social Contribution	Abstract			SID:TaxInstallmentsProgramsDetails1Abstract
1301	Actuarial gains on defined benefit pension plan	Concept (Monetary)	For Period	Debit	SID:IncomeTaxRelatingToRemeasurementsOfDefinedBenefitPlansChargedOrCreditedDirectlyToEquity
1302	Estimated losses for deferred income and social contribution tax credits - actuarial gains	Concept (Monetary)	For Period	Debit	SID:IncomeTaxRelatingToGainsLossesOnRemeasurementsOfDefinedBenefitPlansChargedOrCreditedDirectlyToEquity
1303	Changes in the fair value of assets measured at fair value through other comprehensive income	Concept (Monetary)	For Period	Debit	SID:ChangesInFairValueOfAssetsMeasuredAtFairValueThroughOtherComprehensiveIncome
1304	Estimated losses for deferred income tax and social contribution assets - assets measured at fair value through other comprehensive income	Concept (Monetary)	For Period	Debit	SID:EstimatedLossesForDeferredIncomeTaxAndSocialContributionAssetsAssetsMeasuredAtFairValueThroughOtherComprehensiveIncome
1305	Exchange differences on translating foreign operations	Concept (Monetary)	For Period	Debit	SID:IncomeTaxRelatingToGainsLossesOnExchangeDifferencesOnTranslationChargedOrCreditedDirectlyToEquity
1306	Cash flow hedge accounting	Concept (Monetary)	For Period	Debit	SID:IncomeTaxRelatingToHedgesOfInvestmentsInEquityInstrumentsChargedOrCreditedDirectlyToEquity
1307	Estimated losses for deferred income and social contribution tax credits - cash flow hedge	Concept (Monetary)	For Period	Debit	SID:IncomeTaxRelatingToGainsLossesOnCashFlowHedgesNetOfTaxChargedOrCreditedDirectlyToEquity
1308	Income tax and social contribution	Concept (Monetary)	For Period	Debit	ifrs-full:CurrentAndDeferredTaxRelatingToItemsChargedOrCreditedDirectlyToEquity
1309	00000132 - Disclosure - 16. TAX INSTALLMENTS PROGRAMS (Details)	Network	*	*	http://csn.com.br/role/TaxInstallmentsProgramsDetails
1310	Disclosure of fair value measurement of liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesTable
1311	Classes of liabilities [axis]	Axis			ifrs-full:ClassesOfLiabilitiesAxis
1312	Liabilities [member]	Member			ifrs-full:LiabilitiesMember
1313	Federal REFIS Law 11.941/09	Member			SID:FederalRefisLaw1Member
1314	Federal REFIS Law 12.865/13	Member			SID:FederalRefisLaw2Member
1315	Other taxes in installments	Member			SID:OtherTaxesInInstallmentsMember
1316	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
1317	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
1318	Disclosure of fair value measurement of liabilities [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesLineItems
1319	REFIS debts and other tax installment payment plans, current	Concept (Monetary)	As Of	Credit	SID:RefisAndOtherTaxInstallmentPaymentPlansCurrent
1320	REFIS debts and other tax installment payment plans, noncurrent	Concept (Monetary)	As Of	Credit	SID:RefisAndOtherTaxInstallmentPaymentPlansNoncurrent
1321	00000133 - Disclosure - 17. PROVISION FOR TAX, SOCIAL SECURITY, LABOR, CIVIL AND ENVIRONMENTAL RISKS AND JUDICIAL DEPOSITS (Details)	Network	*	*	http://csn.com.br/role/ProvisionForTaxSocialSecurityLaborCivilAndEnvironmentalRisksAndJudicialDepositsDetails
1322	Disclosure of fair value measurement of liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesTable
1323	Classes of liabilities [axis]	Axis			ifrs-full:ClassesOfLiabilitiesAxis
1324	Liabilities [member]	Member			ifrs-full:LiabilitiesMember
1325	Tax	Member			SID:TaxMember
1326	Social security	Member			SID:SocialSecurityMember
1327	Labor	Member			SID:LaborMember
1328	Civil	Member			SID:CivilMember
1329	Environmental	Member			SID:EnvironmentalMember
1330	Deposit of a guarantee	Member			SID:DepositOfAGuaranteeMember
1331	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
1332	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
1333	Disclosure of fair value measurement of liabilities [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesLineItems
1334	Accrued liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:Accruals
1335	Judicial deposits	Concept (Monetary)	As Of	Credit	ifrs-full:DepositsFromBanks
1336	Provisions for tax, social security, labor and civil risks	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentProvisions
1337	Provision for environmental liabilities and decommissioning of assets	Concept (Monetary)	As Of	Credit	ifrs-full:OtherLongtermProvisions
1338	Deposit from banks	Concept (Monetary)	As Of	Credit	SID:DepositFromBanksNonCurrent
1339	00000134 - Disclosure - 17. PROVISION FOR TAX, SOCIAL SECURITY, LABOR, CIVIL AND ENVIRONMENTAL RISKS AND JUDICIAL DEPOSITS (Details 1)	Network	*	*	http://csn.com.br/role/ProvisionForTaxSocialSecurityLaborCivilAndEnvironmentalRisksAndJudicialDepositsDetails1
1340	Disclosure of fair value measurement of liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesTable
1341	Classes of liabilities [axis]	Axis			ifrs-full:ClassesOfLiabilitiesAxis
1342	Liabilities [member]	Member			ifrs-full:LiabilitiesMember
1343	Tax	Member			SID:TaxMember
1344	Social security	Member			SID:SocialSecurityMember
1345	Labor	Member			SID:LaborMember
1346	Civil	Member			SID:CivilMember
1347	Environmental	Member			SID:EnvironmentalMember
1348	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
1349	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
1350	Disclosure of fair value measurement of liabilities [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesLineItems
1351	Accrued liabilities, beginning	Concept (Monetary)	As Of	Credit	ifrs-full:Accruals
1352	Additions	Concept (Monetary)	For Period	Credit	SID:AdditionsToAccruals
1353	Accrued charges	Concept (Monetary)	For Period	Debit	SID:AccruedCharges
1354	Net utilization of reversal	Concept (Monetary)	For Period	Debit	SID:NetUtilizationOfAccrualReversal
1355	Accrued liabilities, ending	Concept (Monetary)	As Of	Credit	ifrs-full:Accruals
1356	00000135 - Disclosure - 17. PROVISION FOR TAX, SOCIAL SECURITY, LABOR, CIVIL AND ENVIRONMENTAL RISKS AND JUDICIAL DEPOSITS (Details 2)	Network	*	*	http://csn.com.br/role/ProvisionForTaxSocialSecurityLaborCivilAndEnvironmentalRisksAndJudicialDepositsDetails2
1357	Disclosure of fair value measurement of liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesTable
1358	Classes of other provisions [axis]	Axis			ifrs-full:ClassesOfProvisionsAxis
1359	Other provisions	Member			ifrs-full:OtherProvisionsMember
1360	Tax assessment notice issued against the Company for an alleged sale of 40% of the shares of its joint venture NAMISA to a Japanese-Korean consortium	Member			SID:MainLegalMatter1Member
1361	Income tax / Social contribution - Assessment Notice and Imposition of Fine (AIIM) - Disallowance of deductions of goodwill generated in the reverse incorporation of Big Jump by Namisa	Member			SID:MainLegalMatter2Member
1362	Assessment Notice and Imposition of Fine (AIIM) - Income tax / Social contribution - gloss of interest on prepayment arising from supply contracts of iron ore and port services	Member			SID:MainLegalMatter3Member
1363	Assessment Notice and Imposition of Fine (AIIM) - Income tax / Social contribution - Due to profits from foreign subsidiaries (years 2008, 2010 and 2011)	Member			SID:MainLegalMatter4Member
1364	Tax foreclosures - ICMS - Electricity credits	Member			SID:MainLegalMatter5Member
1365	Installments MP 470 - alleged insufficiency of tax losses	Member			SID:MainLegalMatter6Member
1366	Offset of taxes that were not approved by the Federal Revenue Service - IRPJ/CSLL, PIS/COFINS e IPI	Member			SID:MainLegalMatter7Member
1367	Disallowance of the ICMS credits - Transfer of iron ore	Member			SID:MainLegalMatter8Member
1368	ICMS - Refers to the transfer of imported raw material at an amount lower than the price disclosed in the import documentation	Member			SID:MainLegalMatter10Member
1369	Disallowance of the tax losses arising on adjustments to the SAPLI	Member			SID:MainLegalMatter11Member
1370	Assessment Notice - ICMS - shipping and return merchandise for Industrialization	Member			SID:MainLegalMatter12Member
1371	Assessment Notice- Income tax- Capital Gain of CFM vendors located outside	Member			SID:MainLegalMatter13Member
1372	CFEM - Divergence on the understanding between CSN and DNPM on the calculation basis	Member			SID:MainLegalMatter14Member
1373	Other tax (federal, state, and municipal) lawsuits	Member			SID:MainLegalMatter15Member
1374	Assessment Notice - ICMS - Questions about sales to incentive zone	Member			SID:MainLegalMatter21Member
1375	Social security lawsuits	Member			SID:MainLegalMatter16Member
1376	Annulment action filed by CSN against CADE	Member			SID:MainLegalMatter17Member
1377	Other civil lawsuits	Member			SID:MainLegalMatter18Member
1378	Labor and social security lawsuits	Member			SID:MainLegalMatter19Member
1379	Environmental lawsuits - ACP TAC/PAC - Compliance with environmental obligations	Member			SID:MainLegalMatter22Member
1380	Tax foreclosures - Fine of Volta Grande IV (2)	Member			SID:MainLegalMatter23Member
1381	Others Environmental lawsuits	Member			SID:MainLegalMatter20Member
1382	Disclosure of fair value measurement of liabilities [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesLineItems
1383	Legal matters with possible risk of loss	Concept (Monetary)	As Of	Credit	ifrs-full:LegalProceedingsProvision
1384	00000136 - Disclosure - 18. PROVISION FOR ENVIRONMENTAL LIABILITIES AND ASSET RETIREMENT OBLIGATIONS (Details)	Network	*	*	http://csn.com.br/role/ProvisionForEnvironmentalLiabilitiesAndAssetRetirementObligationsDetails
1385	Disclosure of fair value measurement of liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesTable
1386	Classes of liabilities [axis]	Axis			ifrs-full:ClassesOfLiabilitiesAxis
1387	Liabilities [member]	Member			ifrs-full:LiabilitiesMember
1388	Environmental liabilities	Member			SID:EnvironmentalLiabilitiesMember
1389	Asset retirement obligations	Member			SID:AssetRetirementObligationsMember
1390	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
1391	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
1392	Disclosure of fair value measurement of liabilities [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesLineItems
1393	Provision for environmental liabilities and decommissioning of assets	Concept (Monetary)	As Of	Credit	ifrs-full:OtherLongtermProvisions
1394	00000137 - Disclosure - 19. RELATED-PARTY BALANCES AND TRANSACTIONS (Details)	Network	*	*	http://csn.com.br/role/Related-partyBalancesAndTransactionsDetails
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1396	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
1397	Entity [Domain]	Member			dei:EntityDomain
1398	Vicunha Acos	Member			SID:VicunhaAcosSAMember
1399	Rio Iaco Participacoes S.A.	Member			SID:RioLacoParticipacoesSAMember
1400	DisclosureOfRelatedpartyBalancesAndTransactionsLineItems [Line Items]	LineItems			SID:DisclosureOfRelatedpartyBalancesAndTransactionsLineItems
1401	Proposed dividends	Concept (Monetary)	For Period		ifrs-full:DividendsProposedOrDeclaredBeforeFinancialStatementsAuthorisedForIssueButNotRecognisedAsDistributionToOwners
1402	00000138 - Disclosure - 19. RELATED-PARTY BALANCES AND TRANSACTIONS (Details 1)	Network	*	*	http://csn.com.br/role/Related-partyBalancesAndTransactionsDetails1
1403	Disclosure of transactions between related parties [table]	Table	*	*	ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesTable
1404	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
1405	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
1406	Trade receivables	Member			ifrs-full:TradeReceivablesMember
1407	Dividends receivable	Member			SID:DividendsReceivableMember
1408	Actuarial asset	Member			SID:ActuarialAssetMember
1409	Short-term investments/Investments	Member			SID:ShortTermInvestmentsInvestmentsMember
1410	Loans	Member			SID:LoanMember
1411	Other receivables	Member			SID:OtherReceivablesMember
1412	Classes of liabilities [axis]	Axis			ifrs-full:ClassesOfLiabilitiesAxis
1413	Liabilities [member]	Member			ifrs-full:LiabilitiesMember
1414	Accounts payable	Member			SID:AccountPayableMember
1415	Provision for consumption and services	Member			SID:ProvisionForConsumptionAndServicesMember
1416	Trade payables	Member			SID:TradePayablesMember
1417	Actuarial liabilities	Member			SID:ActuarialLiabilitiesMember
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1419	Current assets	Concept (Monetary)	As Of	Debit	SID:CurrentReceivablesDueFromRelatedParties
1420	Noncurrent assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentReceivablesDueFromRelatedParties
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1422	Noncurrent liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPayablesToRelatedParties
1423	Total assets	Concept (Monetary)	As Of	Debit	ifrs-full:AmountsReceivableRelatedPartyTransactions
1424	Total liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:AmountsPayableRelatedPartyTransactions
1425	00000140 - Disclosure - 19. RELATED-PARTY BALANCES AND TRANSACTIONS (Details 3)	Network	*	*	http://csn.com.br/role/Related-partyBalancesAndTransactionsDetails3
1426	Disclosure of transactions between related parties [table]	Table	*	*	ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesTable
1427	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
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1429	Joint Venture/Joint Operation	Member			SID:JointVenturesJointOperationMember
1430	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
1431	Entity [Domain]	Member			dei:EntityDomain
1432	Ita Energetica S.A.	Member			SID:ItaEnergeticaSAMember
1433	MRS Logistica S.A.	Member			SID:MRSLogisticaSAMember
1434	CBSI	Member			SID:CBSIMember
1435	Transnordestina Logistica S.A.	Member			SID:TransnordestinaLogisticaSAMember
1436	CBS Previdencia	Member			SID:CBSPrevidenciaMember
1437	Banco Fibra	Member			SID:BancoFibraMember
1438	Usiminas	Member			SID:UsiminasMember
1439	Panatlantica	Member			SID:PanatlanticaMember
1440	Ibis Participacoes e Servicos	Member			SID:IbisParticipacoesEServicosMember
1441	Other	Member			SID:OtherMember
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1443	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
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1446	Associates	Member			ifrs-full:AssociatesMember
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1448	Current assets	Concept (Monetary)	As Of	Debit	SID:CurrentReceivablesDueFromRelatedParties
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1450	Total assets	Concept (Monetary)	As Of	Debit	ifrs-full:AmountsReceivableRelatedPartyTransactions
1451	Current liabilities	Concept (Monetary)	As Of	Credit	SID:CurrentPayablesToRelatedParties
1452	Noncurrent liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPayablesToRelatedParties
1453	Total liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:AmountsPayableRelatedPartyTransactions
1454	00000141 - Disclosure - 19. RELATED-PARTY BALANCES AND TRANSACTIONS (Details 4)	Network	*	*	http://csn.com.br/role/Related-partyBalancesAndTransactionsDetails4
1455	Disclosure of transactions between related parties [table]	Table	*	*	ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesTable
1456	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
1457	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
1458	Joint Venture/Joint Operation	Member			SID:JointVenturesJointOperationMember
1459	Other Related Parties	Member			ifrs-full:OtherRelatedPartiesMember
1460	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
1461	Entity [Domain]	Member			dei:EntityDomain
1462	Ita Energetica	Member			SID:ItaEnergeticaMember
1463	MRS Logistica	Member			SID:MRSLogisticaMember
1464	CBSI - Companhia Brasileira de Servicos e Infraestrutura	Member			SID:CBSICompanhiaBrasileiraDeServicoseInfraestruturaMember
1465	Transnordestina Logistica S,A	Member			SID:TransnordestinaLogisticaSAMember
1466	CBS Previdencia	Member			SID:CBSPrevidenciaMember
1467	Fundacao CSN	Member			SID:FundacaoCSNMember
1468	Banco Fibra	Member			SID:BancoFibraMember
1469	Usiminas	Member			SID:UsiminasMember
1470	Panatlantica	Member			SID:PanatlanticaMember
1471	Ibis Participacoes e Servicos	Member			SID:IbisParticipacoesEServicosMember
1472	Other	Member			SID:OtherMember
1473	Arvedi Metalfer do Brasil	Member			SID:ArvediMetalferDoBrasilMember
1474	Nacional Minerios S.A.	Member			SID:NacionalMineriosSAMember
1475	Taquari Participacoes S,A	Member			SID:TaquariParticipacoesSAMember
1476	Partfib Projetos Imobiliarios	Member			SID:PartfibProjetosImobiliariosMember
1477	Vicunha Textil S.A.	Member			SID:VicunhaTextilSAMember
1478	Vicunha Servicos Ltda.	Member			SID:VicunhaServicosLtdaMember
1479	Arvedi Metalfer do Brasil S,A,	Member			SID:ArvedMetalferDoBrasilSAMember
1480	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
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1482	Associates	Member			ifrs-full:AssociatesMember
1483	Associates [axis]	Axis			ifrs-full:SignificantInvestmentsInAssociatesAxis
1484	Entity's total for associates [member]	Member			ifrs-full:EntitysTotalForAssociatesMember
1485	Associates	Member			ifrs-full:AssociatesMember
1486	Continuing and discontinued operations [axis]	Axis			ifrs-full:ContinuingAndDiscontinuedOperationsAxis
1487	Continuing operations [member]	Member			ifrs-full:ContinuingOperationsMember
1488	Discontinued operations [member]	Member			ifrs-full:DiscontinuedOperationsMember
1489	Disclosure of transactions between related parties [line items]	LineItems			ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesLineItems
1490	Related party sales	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromSaleOfGoodsRelatedPartyTransactions
1491	Related party purchases	Concept (Monetary)	For Period	Debit	ifrs-full:PurchasesOfGoodsRelatedPartyTransactions
1492	Relared party finance income and costs, net	Concept (Monetary)	For Period	Credit	SID:RelatedPartyFinanceIncomeCost
1493	Foreign exchange and monetary variation, net	Concept (Monetary)	For Period	Credit	SID:IncreaseDecreaseThroughForeignExchangeRelatedPartyTransactions
1494	Related party transactions, net	Concept (Monetary)	For Period	Credit	SID:RelatedPartyTransactionsNet
1495	00000142 - Disclosure - 19. RELATED-PARTY BALANCES AND TRANSACTIONS (Details 5)	Network	*	*	http://csn.com.br/role/Related-partyBalancesAndTransactionsDetails5
1496	Implied Table	Table	*	*	implied:Table
1497	Related-party Balances And Transactions	Abstract			SID:RelatedpartyBalancesAndTransactionsDetails4Abstract
1498	Short-term benefits for employees and officers	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationShorttermEmployeeBenefits
1499	Post-employment benefits	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationPostemploymentBenefits
1500	Key management personnel compensation	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensation
1501	00000143 - Disclosure - 20. SHAREHOLDERS' EQUITY (Details)	Network	*	*	http://csn.com.br/role/ShareholdersEquityDetails
1502	Statement of changes in equity [table]	Table	*	*	ifrs-full:StatementOfChangesInEquityTable
1503	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
1504	Entity [Domain]	Member			dei:EntityDomain
1505	Vicunha Acos S.A.	Member			SID:VicunhaAcosSAMember
1506	Rio Iaco Participacoes S.A.	Member			SID:RioLacoParticipacoesSAMember
1507	NYSE (ADRs)	Member			SID:NyseAdrsMember
1508	Other	Member			SID:OtherMember
1509	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
1510	Equity [member]	Member			ifrs-full:EquityMember
1511	USIM3	Member			SID:USIM3Member
1512	Treasury shares	Member			ifrs-full:TreasurySharesMember
1513	Common	Member			SID:CommonStocksMember
1514	Statement of changes in equity [line items]	LineItems			ifrs-full:StatementOfChangesInEquityLineItems
1515	Number of common shares outstanding	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
1516	Percent of total shares	Concept (Percent)	As Of		SID:PercentageOfShares
1517	Percent of voting capital	Concept (Percent)	As Of		ifrs-full:PercentageOfVotingEquityInterestsAcquired
1518	00000144 - Disclosure - 20. SHAREHOLDERS' EQUITY (Details 1)	Network	*	*	http://csn.com.br/role/ShareholdersEquityDetails1
1519	Statement of changes in equity [table]	Table	*	*	ifrs-full:StatementOfChangesInEquityTable
1520	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
1521	Equity [member]	Member			ifrs-full:EquityMember
1522	Buyback program 1	Member			SID:BuybackProgram1Member
1523	Buyback program 2	Member			SID:BuybackProgram2Member
1524	Buyback program 3	Member			SID:BuybackProgram3Member
1525	Buyback program 4	Member			SID:BuybackProgram4Member
1526	Buyback program 4 (2)	Member			SID:BuybackProgram4Number2Member
1527	Buyback program 5	Member			SID:BuybackProgram5Member
1528	Buyback program 5 (2)	Member			SID:BuybackProgram5Number2Member
1529	Buyback program 6	Member			SID:BuybackProgram6Member
1530	Buyback program 7	Member			SID:BuybackProgram7Member
1531	Buyback program 8	Member			SID:BuybackProgram8Member
1532	Buyback program 9	Member			SID:BuybackProgram9Member
1533	Buyback program 9 (2)	Member			SID:BuybackProgram9Number2Member
1534	Statement of changes in equity [line items]	LineItems			ifrs-full:StatementOfChangesInEquityLineItems
1535	Board's Authorization	Concept (Text/String)	For Period		SID:BoardsAuthorizationDate
1536	Authorized quantity	Concept (Shares)	As Of		ifrs-full:NumberOfSharesAuthorised
1537	Program Period	Concept (Text/String)	For Period		SID:BuybackProgramPeriod
1538	Average buyback price	Concept (Share)	As Of		SID:AverageBuybackPrice
1539	Minimum and maximum buyback price	Concept (Text/String)	For Period		SID:MinimumAndMaximumBuybackPrice
1540	Number bought back	Concept (Shares)	As Of		SID:NumberOfSharesRepurchased
1541	Share cancelation	Concept (Shares)	As Of		SID:NumberOfSharesCancelled
1542	Disposal of shares	Concept (Shares)	As Of		SID:DisposalOfShares
1543	Balance in treasury	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
1544	00000145 - Disclosure - 20. SHAREHOLDERS' EQUITY (Details 2)	Network	*	*	http://csn.com.br/role/ShareholdersEquityDetails2
1545	Implied Table	Table	*	*	implied:Table
1546	Shareholders Equity	Abstract			SID:ShareholdersEquityDetails2Abstract
1547	Treasury share purchased	Concept (Shares)	As Of		SID:NumberOfSharesRepurchased
1548	Amount paid for treasury share	Concept (Monetary)	As Of	Debit	ifrs-full:TreasuryShares
1549	Minimum share price	Concept (Share)	As Of		SID:MinimumBuybackPrice
1550	Maximum share price	Concept (Share)	As Of		SID:MaximumBuybackPrice
1551	Average share price	Concept (Share)	As Of		SID:AverageBuybackPrice
1552	Treasury share market price	Concept (Monetary)	As Of	Debit	SID:TreasurySharesMarketPrice
1553	00000146 - Disclosure - 20. SHAREHOLDERS' EQUITY (Details 3)	Network	*	*	http://csn.com.br/role/ShareholdersEquityDetails3
1554	Implied Table	Table	*	*	implied:Table
1555	Shareholders Equity	Abstract			SID:ShareholdersEquityDetails3Abstract
1556	(Loss) profit for the year	Abstract			ifrs-full:ProfitLossAbstract
1557	Continued operations	Concept (Monetary)	For Period	Credit	SID:ProfitLossFromContinuedOperations
1558	Discontinued operations	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromDiscontinuedOperations
1559	(Loss) profit for the year	Concept (Monetary)	For Period	Credit	SID:ProfitLossAttributableToOwners
1560	Weighted average number of shares	Concept (Shares)	For Period		ifrs-full:WeightedAverageShares
1561	Basic and diluted EPS	Abstract			ifrs-full:BasicAndDilutedEarningsPerShareAbstract
1562	Continued Operations	Concept (Share)	For Period		ifrs-full:BasicAndDilutedEarningsLossPerShareFromContinuingOperations
1563	Discontinued Operations	Concept (Share)	For Period		ifrs-full:BasicAndDilutedEarningsLossPerShareFromDiscontinuedOperations
1564	Basic and diluted EPS	Concept (Share)	For Period		ifrs-full:BasicAndDilutedEarningsLossPerShare
1565	00000147 - Disclosure - 20. SHAREHOLDERS' EQUITY (Details Narrative)	Network	*	*	http://csn.com.br/role/ShareholdersEquityDetailsNarrative
1566	Implied Table	Table	*	*	implied:Table
1567	Shareholders Equity	Abstract			SID:ShareholdersEquityDetailsNarrativeAbstract
1568	Issued capital	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
1569	Number of common shares outstanding	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
1570	00000148 - Disclosure - 21. PAYMENT TO SHAREHOLDERS (Details)	Network	*	*	http://csn.com.br/role/PaymentToShareholdersDetails
1571	Implied Table	Table	*	*	implied:Table
1572	Payment To Shareholders	Abstract			SID:PaymentToShareholdersDetailsAbstract
1573	Profit for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOwnersOfParent
1574	Absorption of deficits	Concept (Monetary)	For Period	Debit	SID:AbsorptionOfDeficits
1575	Legal reserve	Concept (Monetary)	For Period	Debit	SID:LegalReserve
1576	Allocation of profits	Concept (Monetary)	For Period	Credit	SID:AllocationOfProfits
1577	Proposed destination:	Abstract			SID:PaymentToShareholdersProposedDestinationAbstract
1578	Mandatory minimum dividends	Concept (Monetary)	For Period	Debit	SID:MandatoryMinimumDividends
1579	Intended for statutory reserve of working capital	Concept (Monetary)	For Period	Debit	SID:IntendedForStatutoryReserveOfWorkingCapital
1580	In current liabilities	Abstract			SID:PaymentToShareholdersInCurrentLiabilitiesAbstract
1581	Dividends to be paid on December 31, 2017	Concept (Monetary)	As Of	Credit	ifrs-full:DividendsPayable
1582	Mandatory minimum dividends	Concept (Monetary)	For Period	Debit	SID:MandatoryMinimumDividends
1583	Dividends to be paid on December 31, 2018	Concept (Monetary)	As Of	Credit	ifrs-full:DividendsPayable
1584	Weighted average number of shares	Concept (Shares)	For Period		SID:WeightedAverageNumberOfShares
1585	Dividends per share approved	Concept (Share)	For Period		SID:DividendsPerShareApproved
1586	00000150 - Disclosure - 22. NET SALES AND SERVICES REVENUE (Details)	Network	*	*	http://csn.com.br/role/NetSalesAndServicesRevenueDetails
1587	Disclosure of disaggregation of revenue from contracts with customers [table]	Table	*	*	ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersTable
1588	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
1589	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
1590	Domestic market	Member			SID:DomesticMarketMember
1591	Foreign market	Member			SID:ForeignMarketMember
1592	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
1593	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
1594	Disclosure of disaggregation of revenue from contracts with customers [line items]	LineItems			ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems
1595	Gross revenue	Concept (Monetary)	For Period	Credit	SID:GrossRevenue
1596	Sales returns and discounts	Concept (Monetary)	For Period	Debit	SID:SalesReturnsAndDiscounts
1597	Taxes on sales	Concept (Monetary)	For Period	Debit	SID:TaxEffectOfRevenues
1598	Deductions	Concept (Monetary)	For Period	Debit	SID:RevenueDeductions
1599	Net revenues	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
1600	00000152 - Disclosure - 23. EXPENSES BY NATURE (Details 1)	Network	*	*	http://csn.com.br/role/ExpensesByNatureDetails1
1601	Implied Table	Table	*	*	implied:Table
1602	Expenses By Nature	Abstract			SID:ExpensesByNatureDetails1Abstract
1603	Production costs	Concept (Monetary)	For Period	Debit	SID:ProductionCost
1604	Sales expenses	Concept (Monetary)	For Period	Debit	ifrs-full:SellingExpense
1605	General and Administrative Expenses	Concept (Monetary)	For Period	Debit	ifrs-full:GeneralAndAdministrativeExpense
1606	Depreciation, amortization and depletion	Concept (Monetary)	For Period	Debit	ifrs-full:OperatingExpense
1607	Other operating expenses	Concept (Monetary)	For Period	Debit	ifrs-full:MiscellaneousOtherOperatingExpense
1608	Total	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseByNature
1609	00000155 - Disclosure - 26. SEGMENT INFORMATION (Details)	Network	*	*	http://csn.com.br/role/SegmentInformationDetails
1610	Disclosure of operating segments [table]	Table	*	*	ifrs-full:DisclosureOfOperatingSegmentsTable
1611	Segments [axis]	Axis			ifrs-full:SegmentsAxis
1612	Segments [member]	Member			ifrs-full:SegmentsMember
1613	Steel	Member			SID:SteelMember
1614	Mining	Member			SID:MiningMember
1615	Port	Member			SID:PortMember
1616	Railroads	Member			SID:RailroadsMember
1617	Energy	Member			SID:EnergyMember
1618	Cement	Member			SID:CementMember
1619	Corporate expenses/elimination	Member			SID:CorporateExpensesEliminationMember
1620	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
1621	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
1622	Domestic market	Member			SID:DomesticMarketMember
1623	Foreign market	Member			SID:ForeignMarketMember
1624	Disclosure of operating segments [line items]	LineItems			ifrs-full:DisclosureOfOperatingSegmentsLineItems
1625	Metric tons (Thou.)	Concept (Text/String)	For Period		SID:VolumeOfMiningAsset
1626	Net revenues	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
1627	Cost of sales and services	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
1628	Gross profit	Concept (Monetary)	For Period	Credit	ifrs-full:GrossProfit
1629	General and administrative expenses	Concept (Monetary)	For Period	Debit	SID:GeneralAndAdministrativeExpenses
1630	Depreciation	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationExpense
1631	Proportionate EBITDA of joint ventures	Concept (Monetary)	For Period	Credit	SID:ProportionateEbitdaOfJointVentures
1632	Adjusted EBITDA	Concept (Monetary)	For Period	Credit	SID:AdjustedEbitda
1633	00000156 - Disclosure - 26. SEGMENT INFORMATION (Details 1)	Network	*	*	http://csn.com.br/role/SegmentInformationDetails1
1634	Implied Table	Table	*	*	implied:Table
1635	Segment Information	Abstract			SID:SegmentInformationDetails1Abstract
1636	Net income / (loss) for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
1637	Result from discontinued operations with the following value 9,561	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromDiscontinuedOperations
1638	Depreciation / amortization / depletion (note 23)	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
1639	Income tax and social contribution (note 15)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
1640	Financial income / (expenses) (note 25)	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncomeCost
1641	EBITDA	Concept (Monetary)	For Period	Credit	SID:Ebitda
1642	Other operating (income) / expenses (note 24)	Concept (Monetary)	For Period	Credit	SID:MiscellaneousOtherOperatingIncomeExpense
1643	Equity in results of affiliated companies	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfAssociatesAccountedForUsingEquityMethod
1644	Proportionate EBITDA of joint ventures	Concept (Monetary)	For Period	Credit	SID:ProportionateEbitdaOfJointVentures
1645	Adjusted EBITDA (*)	Concept (Monetary)	For Period	Credit	SID:AdjustedEbitda
1646	00000157 - Disclosure - 27. EMPLOYEE BENEFITS (Details)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails
1647	Disclosure of fair value of plan assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueOfPlanAssetsTable
1648	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1649	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1650	Pension plan benefits	Member			SID:PensionPlanBenefitsMember
1651	Post-employment healthcare benefits	Member			SID:PostEmploymentHealthcareBenefitsMember
1652	Consolidation Items [Axis]	Axis			srt:ConsolidationItemsAxis
1653	Consolidation Items [Domain]	Member			srt:ConsolidationItemsDomain
1654	Disclosure of fair value of plan assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueOfPlanAssetsLineItems
1655	Actuarial assets	Concept (Monetary)	As Of	Debit	ifrs-full:AssetsOfBenefitPlan
1656	Actuarial liabilities	Concept (Monetary)	As Of	Credit	SID:LiabilitiesOfBenefitPlan
1657	00000158 - Disclosure - 27. EMPLOYEE BENEFITS (Details 1)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails1
1658	Implied Table	Table	*	*	implied:Table
1659	Employee Benefits	Abstract			SID:EmployeeBenefitsDetails1Abstract
1660	Present value of defined benefit obligation	Concept (Monetary)	As Of	Credit	ifrs-full:DefinedBenefitObligationAtPresentValue
1661	Fair value of plan assets	Concept (Monetary)	As Of	Debit	ifrs-full:PlanAssetsAtFairValue
1662	Deficit (Surplus)	Concept (Monetary)	As Of	Debit	ifrs-full:SurplusDeficitInPlan
1663	Restriction to actuarial assets due to recovery limitation	Concept (Monetary)	As Of	Debit	SID:RestrictionToActuarialAssetsDueToRecoveryLimitation
1664	Liabilities (Assets), net	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilityAssetOfDefinedBenefitPlans
1665	Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentRecognisedLiabilitiesDefinedBenefitPlan
1666	Assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentRecognisedAssetsDefinedBenefitPlan
1667	(Assets) liabilities recognized in the balance sheet	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilityAssetOfDefinedBenefitPlans
1668	00000159 - Disclosure - 27. EMPLOYEE BENEFITS (Details 2)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails2
1669	Implied Table	Table	*	*	implied:Table
1670	Employee Benefits	Abstract			SID:EmployeeBenefitsDetails2Abstract
1671	Present value of defined benefit obligation, beginning	Concept (Monetary)	As Of	Credit	ifrs-full:DefinedBenefitObligationAtPresentValue
1672	Cost of service	Concept (Monetary)	For Period	Credit	ifrs-full:CurrentServiceCostNetDefinedBenefitLiabilityAsset
1673	Interest cost	Concept (Monetary)	For Period	Credit	ifrs-full:InterestExpenseIncomeNetDefinedBenefitLiabilityAsset
1674	Benefits paid	Concept (Monetary)	For Period	Debit	ifrs-full:BenefitsPaidOrPayable
1675	Actuarial loss/(gain)	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughOtherChangesNetDefinedBenefitLiabilityAsset
1676	Present value of defined benefit obligation, ending	Concept (Monetary)	As Of	Credit	ifrs-full:DefinedBenefitObligationAtPresentValue
1677	00000160 - Disclosure - 27. EMPLOYEE BENEFITS (Details 3)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails3
1678	Implied Table	Table	*	*	implied:Table
1679	Employee Benefits	Abstract			SID:EmployeeBenefitsDetails3Abstract
1680	Fair value of plan assets, beginning	Concept (Monetary)	As Of	Debit	ifrs-full:PlanAssetsAtFairValue
1681	Interest income	Concept (Monetary)	For Period	Credit	SID:InterestIncomeNetDefinedBenefitLiabilityAsset
1682	Benefits paid	Concept (Monetary)	For Period	Debit	ifrs-full:BenefitsPaidOrPayable
1683	Expected return on plan assets (less interest income)	Concept (Monetary)	For Period	Debit	ifrs-full:ReturnOnPlanAssetsNetDefinedBenefitLiabilityAsset
1684	Fair value of plan assets, ending	Concept (Monetary)	As Of	Debit	ifrs-full:PlanAssetsAtFairValue
1685	00000161 - Disclosure - 27. EMPLOYEE BENEFITS (Details 4)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails4
1686	Implied Table	Table	*	*	implied:Table
1687	Employee Benefits	Abstract			SID:EmployeeBenefitsDetails4Abstract
1688	Cost of current service	Concept (Monetary)	For Period	Credit	ifrs-full:CurrentServiceCostNetDefinedBenefitLiabilityAsset
1689	Interest cost	Concept (Monetary)	For Period	Credit	ifrs-full:InterestExpenseIncomeNetDefinedBenefitLiabilityAsset
1690	Expected return on plan assets	Concept (Monetary)	For Period	Debit	SID:ExpectedReturnOnPlanAssetsNetDefinedBenefitLiabilityAsset
1691	Interest on the asset ceiling effect	Concept (Monetary)	For Period	Debit	ifrs-full:GainLossOnChangesInEffectOfLimitingNetDefinedBenefitAssetToAssetCeiling
1692	Total	Concept (Monetary)	For Period	Credit	SID:IncomeExpenseFromDefinedBenefitObligation
1693	Total unrecognized costs / (income) (*)	Concept (Monetary)	For Period	Credit	SID:UnrecognisedIncomeExpenseFromDefinedBenefitObligation
1694	Total costs / (income) recognized in the income statement	Concept (Monetary)	For Period	Credit	SID:RecognisedIncomeExpenseFromDefinedBenefitObligation
1695	Total costs / (income), net (*)	Concept (Monetary)	For Period	Credit	SID:IncomeExpenseFromDefinedBenefitObligation
1696	00000162 - Disclosure - 27. EMPLOYEE BENEFITS (Details 5)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails5
1697	Implied Table	Table	*	*	implied:Table
1698	Employee Benefits	Abstract			SID:EmployeeBenefitsDetails5Abstract
1699	Actuarial losses and (gains)	Concept (Monetary)	For Period	Debit	SID:ActuarialGainsLossesDefinedBenefitLiabilityAsset
1700	Return on plan assets (less interest income)	Concept (Monetary)	For Period	Debit	ifrs-full:ReturnOnPlanAssetsNetDefinedBenefitLiabilityAsset
1701	Total	Concept (Monetary)	For Period	Debit	ifrs-full:GainLossOnRemeasurementOfNetDefinedBenefitLiabilityAsset
1702	Actuarial losses and (gains) recognized in other comprehensive income	Concept (Monetary)	For Period	Debit	SID:RecognisedGainLossOnRemeasurementOfNetDefinedBenefitLiabilityAsset
1703	Unrecognized actuarial (gains)	Concept (Monetary)	For Period	Debit	SID:UnrecognisedGainLossOnRemeasurementOfNetDefinedBenefitLiabilityAsset
1704	Total	Concept (Monetary)	For Period	Debit	SID:GainLossOnRemeasurementNetDefinedBenefitLiabilityAsset
1705	00000163 - Disclosure - 27. EMPLOYEE BENEFITS (Details 6)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails6
1706	Implied Table	Table	*	*	implied:Table
1707	Employee Benefits	Abstract			SID:EmployeeBenefitsDetails6Abstract
1708	Loss due to change in demographic assumptions	Concept (Monetary)	For Period	Debit	ifrs-full:ActuarialGainsLossesArisingFromChangesInDemographicAssumptionsNetDefinedBenefitLiabilityAsset
1709	Loss due to change in financial assumptions	Concept (Monetary)	For Period	Debit	ifrs-full:ActuarialGainsLossesArisingFromChangesInFinancialAssumptionsNetDefinedBenefitLiabilityAsset
1710	Loss due to experience adjustments	Concept (Monetary)	For Period	Debit	ifrs-full:ActuarialGainsLossesArisingFromExperienceAdjustmentsNetDefinedBenefitLiabilityAsset
1711	Return on plan assets (less interest income)	Concept (Monetary)	For Period	Debit	ifrs-full:ReturnOnPlanAssetsNetDefinedBenefitLiabilityAsset
1712	Actuarial losses and (gains)	Concept (Monetary)	For Period	Debit	ifrs-full:GainLossOnRemeasurementOfNetDefinedBenefitLiabilityAsset
1713	00000164 - Disclosure - 27. EMPLOYEE BENEFITS (Details 7)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails7
1714	Implied Table	Table	*	*	implied:Table
1715	Employee Benefits	Abstract			SID:EmployeeBenefitsDetails7Abstract
1716	Actuarial financing method	Concept (Text/String)	For Period		SID:DescriptionOfActuarialFinancingMethod
1717	Functional currency	Concept (Text/String)	For Period		ifrs-full:DescriptionOfFunctionalCurrency
1718	Recognition of plan assets	Concept (Text/String)	For Period		SID:DescriptionOfRecognitionOfPlanAssets
1719	Nominal discount rate	Concept (Text/String)	For Period		SID:ActuarialAssumptionOfNominalDiscountRates
1720	Inflation rate	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfExpectedRatesOfInflation
1721	Nominal salary increase rate	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfExpectedRatesOfSalaryIncreases
1722	Nominal benefit increase rate	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfExpectedRatesOfPensionIncreases
1723	Rate of return on investments	Concept (Text/String)	For Period		SID:ActuarialAssumptionOfRateOfReturnsOnInvestments
1724	General mortality table	Concept (Text/String)	For Period		SID:GeneralMortalityTableDescription
1725	Disability table	Concept (Text/String)	For Period		SID:DisabilityTableDescription
1726	Disability mortality table	Concept (Text/String)	For Period		SID:DisabilityMortalityTableDescription
1727	Turnover table	Concept (Text/String)	For Period		SID:TurnoverTableDescription
1728	Retirement age	Concept (Text/String)	For Period		SID:DescriptionOfRetirementAge
1729	Household composition of active participants	Concept (Text/String)	For Period		SID:DescriptionOfHouseholdOfActiveParticipants
1730	00000165 - Disclosure - 27. EMPLOYEE BENEFITS (Details 8)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails8
1731	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1732	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1733	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1734	Plan covering 35% of the average salary	Member			SID:PlanCoveringThrityFivePercentOfTheAverageSalary1Member
1735	Average salary supplementation plan	Member			SID:AverageSalarySupplementationPlan1Member
1736	Milenio Plan	Member			SID:MilenioPlanMember
1737	Range [Axis]	Axis			ifrs-full:RangeAxis
1738	Ranges [member]	Member			ifrs-full:RangesMember
1739	Male	Member			SID:MaleMember
1740	Female	Member			SID:FemaleMember
1741	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
1742	Average life expectancy of employees (in years)	Concept (Text/String)	For Period		SID:AverageLifeExpectancyOfEmployees
1743	Average life expectancy in years of employees who are 40 (in years)	Concept (Text/String)	For Period		SID:AverageLifeExpectancyOfEmployeesThatAreForty
1744	00000166 - Disclosure - 27. EMPLOYEE BENEFITS (Details 9)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails9
1745	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1746	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1747	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1748	Variable income	Member			SID:VariableIncomeMember
1749	Fixed income	Member			SID:FixedIncomeMember
1750	Real estate	Member			SID:RealEstateAssetMember
1751	Others	Member			SID:OthersMember
1752	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
1753	Allocation of plan assets	Concept (Monetary)	As Of	Debit	ifrs-full:PlanAssetsAtFairValue
1754	Allocation of plan assets percent	Concept (Percent)	As Of		SID:PlanAssetsPercentage
1755	00000167 - Disclosure - 27. EMPLOYEE BENEFITS (Details 10)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails10
1756	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1757	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1758	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
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1760	Plan covering 35% of the average salary	Member			SID:PlanCoveringThrityFivePercentOfTheAverageSalary2Member
1761	Average salary supplementation plan	Member			SID:AverageSalarySupplementationPlan1Member
1762	Average salary supplementation plan	Member			SID:AverageSalarySupplementationPlan2Member
1763	Mixed supplementary benefit plan (Milenio Plan)	Member			SID:MixedSupplementaryBenefitPlan1Member
1764	Mixed supplementary benefit plan (Milenio Plan)	Member			SID:MixedSupplementaryBenefitPlan2Member
1765	Actuarial assumptions [axis]	Axis			ifrs-full:ActuarialAssumptionsAxis
1766	Actuarial assumptions [member]	Member			ifrs-full:ActuarialAssumptionsMember
1767	Discount rate	Member			ifrs-full:ActuarialAssumptionOfDiscountRatesMember
1768	Salary growth	Member			ifrs-full:ActuarialAssumptionOfExpectedRatesOfSalaryIncreasesMember
1769	Mortality table	Member			SID:ActuarialAssumptionOfMortalityMember
1770	Benefit adjustment	Member			ifrs-full:OtherMaterialActuarialAssumptionsMember
1771	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
1772	Sensitivity level	Concept (Percent)	For Period		SID:SensitivityLevel
1773	Effect on current service cost and on interest on actuarial obligations	Concept (Monetary)	For Period	Credit	ifrs-full:PastServiceCostNetDefinedBenefitLiabilityAsset
1774	Effect on present value of obligations	Concept (Monetary)	For Period	Debit	ifrs-full:ReturnOnPlanAssetsNetDefinedBenefitLiabilityAsset
1775	00000168 - Disclosure - 27. EMPLOYEE BENEFITS (Details 11)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails11
1776	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1777	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1778	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1779	Year 1	Member			SID:Year1Member
1780	Year 2	Member			SID:Year2Member
1781	Year 3	Member			SID:Year3Member
1782	Year 4	Member			SID:Year4Member
1783	Year 5	Member			SID:Year5Member
1784	Next 5 years	Member			SID:Next5YearsMember
1785	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
1786	Benefit payments of the defined benefit plans	Concept (Monetary)	For Period	Debit	ifrs-full:PaymentsFromPlanNetDefinedBenefitLiabilityAsset
1787	00000169 - Disclosure - 27. EMPLOYEE BENEFITS (Details 12)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails12
1788	Disclosure of net defined benefit liability (asset) [table]	Table	*	*	ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetTable
1789	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1790	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1791	Post-employment healthcare benefits	Member			SID:PostEmploymentHealthcareBenefitsMember
1792	Disclosure of net defined benefit liability (asset) [line items]	LineItems			ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetLineItems
1793	Present value of obligations	Concept (Monetary)	As Of	Credit	ifrs-full:DefinedBenefitObligationAtPresentValue
1794	Actuarial liabilities	Concept (Monetary)	As Of	Credit	SID:LiabilitiesOfBenefitPlan
1795	00000170 - Disclosure - 27. EMPLOYEE BENEFITS (Details 13)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails13
1796	Disclosure of net defined benefit liability (asset) [table]	Table	*	*	ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetTable
1797	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1798	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1799	Post-employment healthcare benefits	Member			SID:PostEmploymentHealthcareBenefitsMember
1800	Disclosure of net defined benefit liability (asset) [line items]	LineItems			ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetLineItems
1801	Actuarial liability at the beginning of the year	Concept (Monetary)	As Of	Credit	SID:LiabilitiesOfBenefitPlan
1802	Expenses recognized in income for the year	Concept (Monetary)	For Period	Credit	SID:ExpensesRecognizedInIncomeNetDefinedBenefitLiability
1803	Sponsor's contributions transferred in prior year	Concept (Monetary)	For Period	Debit	SID:SponsorsContributionsTransferredInPriorYearNetDefinedBenefitLiability
1804	Recognition of actuarial loss/ (gain)	Concept (Monetary)	For Period	Credit	SID:RecognitionOfLossGainNetDefinedBenefitLiability
1805	Actuarial liability at the end of the year	Concept (Monetary)	As Of	Credit	SID:LiabilitiesOfBenefitPlan
1806	00000171 - Disclosure - 27. EMPLOYEE BENEFITS (Details 14)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails14
1807	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1808	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1809	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1810	Post-employment healthcare benefits	Member			SID:PostEmploymentHealthcareBenefitsMember
1811	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
1812	Actuarial gain (loss) on obligation	Concept (Monetary)	For Period	Debit	SID:ActuarialGainsLossesDefinedBenefitLiabilityAsset
1813	Gain (loss) recognized in shareholders' equity	Concept (Monetary)	For Period	Debit	ifrs-full:GainLossOnRemeasurementOfNetDefinedBenefitLiabilityAsset
1814	00000172 - Disclosure - 27. EMPLOYEE BENEFITS (Details 15)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails15
1815	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1816	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1817	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1818	Post-employment healthcare benefits	Member			SID:PostEmploymentHealthcareBenefitsMember
1819	Range [Axis]	Axis			ifrs-full:RangeAxis
1820	Ranges [member]	Member			ifrs-full:RangesMember
1821	Male	Member			SID:MaleMember
1822	Female	Member			SID:FemaleMember
1823	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
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1825	Average life expectancy in years of employees who are 40 (in years)	Concept (Text/String)	For Period		SID:AverageLifeExpectancyOfEmployeesThatAreForty
1826	00000173 - Disclosure - 27. EMPLOYEE BENEFITS (Details 16)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails16
1827	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1828	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1829	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1830	Post-employment healthcare benefits	Member			SID:PostEmploymentHealthcareBenefitsMember
1831	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
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1833	Disability mortality table	Concept (Text/String)	For Period		SID:DisabilityMortalityTableDescription
1834	Actuarial nominal discount rate	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfDiscountRates
1835	Inflation	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfExpectedRatesOfInflation
1836	Real increase in medical costs based on age (Aging Factor)	Concept (Text/String)	For Period		SID:ActuarialAssumptionOfMedicalCostTrendRatesBasedOnAge
1837	Nominal increase medical costs growth rate	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfMedicalCostTrendRates
1838	Average medical cost	Concept (Text/String)	For Period		SID:AverageMedicalCost
1839	00000174 - Disclosure - 27. EMPLOYEE BENEFITS (Details 17)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails17
1840	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1841	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1842	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1843	Post-employment healthcare benefits	Member			SID:PostEmploymentHealthcareBenefits1Member
1844	Post-employment healthcare benefits	Member			SID:PostEmploymentHealthcareBenefits2Member
1845	Actuarial assumptions [axis]	Axis			ifrs-full:ActuarialAssumptionsAxis
1846	Actuarial assumptions [member]	Member			ifrs-full:ActuarialAssumptionsMember
1847	Discount rate	Member			ifrs-full:ActuarialAssumptionOfDiscountRatesMember
1848	Medical inflation	Member			ifrs-full:ActuarialAssumptionOfMedicalCostTrendRatesMember
1849	Mortality table	Member			SID:ActuarialAssumptionOfMortalityMember
1850	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
1851	Sensitivity level	Concept (Percent)	For Period		SID:SensitivityLevel
1852	Effect on current service cost and on interest on actuarial obligations	Concept (Monetary)	For Period	Credit	ifrs-full:PastServiceCostNetDefinedBenefitLiabilityAsset
1853	Effect on present value of obligations	Concept (Monetary)	For Period	Debit	ifrs-full:ReturnOnPlanAssetsNetDefinedBenefitLiabilityAsset
1854	00000175 - Disclosure - 27. EMPLOYEE BENEFITS (Details 18)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetails18
1855	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1856	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1857	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1858	Post-employment healthcare benefits	Member			SID:PostEmploymentHealthcareBenefitsMember
1859	Range [Axis]	Axis			ifrs-full:RangeAxis
1860	Ranges [member]	Member			ifrs-full:RangesMember
1861	Year 1	Member			SID:Year1Member
1862	Year 2	Member			SID:Year2Member
1863	Year 3	Member			SID:Year3Member
1864	Year 4	Member			SID:Year4Member
1865	Year 5	Member			SID:Year5Member
1866	Next 5 years	Member			SID:Next5YearsMember
1867	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
1868	Benefit payments of the defined benefit plans	Concept (Monetary)	For Period	Debit	ifrs-full:PaymentsFromPlanNetDefinedBenefitLiabilityAsset
1869	00000176 - Disclosure - 27. EMPLOYEE BENEFITS (Details Narrative)	Network	*	*	http://csn.com.br/role/EmployeeBenefitsDetailsNarrative
1870	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
1871	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1872	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1873	Active contributors	Member			SID:ActiveContributorsMember
1874	Retired employees	Member			SID:RetiredEmployeesMember
1875	Related beneficiaries	Member			SID:RelatedBeneficiariesMember
1876	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
1877	Total participants	Concept (Decimal)	For Period		ifrs-full:NumberOfParticipantsOfRetirementBenefitPlanReceivingBenefits
1878	Pension plan expense	Concept (Monetary)	For Period	Debit	SID:PensionPlanExpense
1879	00000177 - Disclosure - 28. COMMITMENTS (Details)	Network	*	*	http://csn.com.br/role/CommitmentsDetails
1880	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1881	Types of contracts [axis]	Axis			ifrs-full:TypesOfContractsAxis
1882	Types of contracts [member]	Member			ifrs-full:TypesOfContractsMember
1883	Transportation of iron ore, coal, coke, steel products, cement and mining products	Member			SID:TransportationOfIronOreCoalCokeSteelProductsCementAndMiningProductsMember
1884	Supply of power, natural gas, oxygen, nitrogen, argon and iron ore pellets	Member			SID:SupplyOfPowerNaturalGasOxygenNitrogenArgonAndIronOrePelletsMember
1885	Processing of furnace sludge and slag generated during pig iron and steel production	Member			SID:ProcessingOfSlagGeneratedDuringPigIronAndSteelProductionMember
1886	Manufacturing, repair, recovery and production of ingot casting machine units	Member			SID:ManufacturingRepairRecoveryAndProductionOfIngotCastingMachineUnitsMember
1887	Range [Axis]	Axis			ifrs-full:RangeAxis
1888	Ranges [member]	Member			ifrs-full:RangesMember
1889	2017	Member			SID:TwentySeventeenMember
1890	2018	Member			SID:TwentyEighteenMember
1891	2019	Member			SID:TwentyNineteenMember
1892	2020	Member			SID:TwentyTwentyMember
1893	2021	Member			SID:TwentyTwentyOneMember
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1895	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1896	Take-or-pay contracts	Concept (Monetary)	As Of	Credit	ifrs-full:CapitalCommitments
1897	00000178 - Disclosure - 28. COMMITMENTS (Details 1)	Network	*	*	http://csn.com.br/role/CommitmentsDetails1
1898	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1899	Types of contracts [axis]	Axis			ifrs-full:TypesOfContractsAxis
1900	Types of contracts [member]	Member			ifrs-full:TypesOfContractsMember
1901	FTL	Member			SID:FTLMember
1902	Tecar	Member			SID:TecarMember
1903	Tecon	Member			SID:TeconMember
1904	Range [Axis]	Axis			ifrs-full:RangeAxis
1905	Ranges [member]	Member			ifrs-full:RangesMember
1906	2019	Member			SID:TwentyNineteenMember
1907	2020	Member			SID:TwentyTwentyMember
1908	2021	Member			SID:TwentyTwentyOneMember
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1910	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1911	Type of service	Concept (Text/String)	For Period		SID:DescriptionOfTypesOfService
1912	Minimum future payments related to government concessions	Concept (Monetary)	As Of	Credit	ifrs-full:MinimumLeasePaymentsPayableUnderNoncancellableOperatingLease
1913	00000179 - Disclosure - 30. ADDITIONAL INFORMATION TO CASH FLOWS (Details)	Network	*	*	http://csn.com.br/role/AdditionalInformationToCashFlowsDetails
1914	Implied Table	Table	*	*	implied:Table
1915	Additional Information To Cash Flows	Abstract			SID:AdditionalInformationToCashFlowsDetailsAbstract
1916	Income tax and social contribution paid	Concept (Monetary)	For Period	Credit	ifrs-full:IncomeTaxesPaidRefund
1917	Addition to PP&E with interest capitalization	Concept (Monetary)	For Period	Debit	ifrs-full:AdditionsOtherThanThroughBusinessCombinationsPropertyPlantAndEquipment
1918	Acquisition of fixed assets through loans	Concept (Monetary)	For Period	Credit	SID:PurchaseOfPropertyPlantAndEquipmentThroughLoans
1919	Non-monetary transaction with joint venture	Concept (Monetary)	For Period	Credit	SID:CapitalizationWithAdvanceToFutureCapitalIncrease
1920	Total additional information to cash flows	Concept (Monetary)	For Period	Debit	SID:AdditionalCashFlows