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8 Financial investments (Details Narrative)	12 Months Ended
	Dec. 31, 2020
Certificado de deposito interbancario [member]
FinancialInvestmentsLineItems [Line Items]
Average yield of financial investments	98.95%

X

- Definition

Percentage of average yield of financial instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	sbs_
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Balance Type:	na
Period Type:	duration

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- References

No definition available.

+ Details

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Namespace Prefix:	sbs_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: