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v3.21.1

7 Cash and cash equivalents (Details Narrative) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Certificado de deposito interbancario [member] |  |
CashAndCashEquivalentLineItems [Line Items] |  |
Average yield of cash equivalents | 95.82% | 98.02%

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- Definition It represents the average yield of cash equivalents. + References No definition available. + Details
Name: | sbs_AverageYieldOfCashEquivalents
Namespace Prefix: | sbs_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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

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- Details
Name: | ifrs-full_TypesOfInterestRatesAxis=sbs_CertificadoDeDepositoInterbancarioMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |