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26 EMPLOYEE BENEFITS (Details 15) - Post-employment Healthcare Benefits [Member] | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Male [Member] |  |
EmployeeBenefitsLineItems [Line Items] |  |
Average life expectancy of employees (in years) | 20.24 | 19.55
Average life expectancy in years of employees who are 40 (in years) | 42.74 | 41.59
Female [Member] |  |
EmployeeBenefitsLineItems [Line Items] |  |
Average life expectancy of employees (in years) | 20.24 | 22.17
Average life expectancy in years of employees who are 40 (in years) | 42.74 | 45.30

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- Definition Represents the information about average life expectancy in years of employees who are 65. + References No definition available. + Details
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Namespace Prefix: | sid_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the information about average life expectancy in years of employees who are 40. + References No definition available. + Details
Name: | sid_AverageLifeExpectancyOfEmployeesThatAreForty
Namespace Prefix: | sid_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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- Details
Name: | ifrs-full_DefinedBenefitPlansAxis=sid_PostEmploymentHealthcareBenefitsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | sid_ParticipantsAxis=sid_MaleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | sid_ParticipantsAxis=sid_FemaleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |