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

It represents the average yield of cash equivalents.

No definition available.

Name:	sbs_AverageYieldOfCashEquivalents
Namespace Prefix:	sbs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration