21 Employees benefits (Details 5) R$ in Thousands	12 Months Ended
Dec. 31, 2020 BRL (R$)
G1 Plan [member]
Summary of employee benefits [Line Items]
Payment of benefits expected in 2021	R$ 177,347
Payment of benefits expected in 2022	172,477
Payment of benefits expected in 2023	167,906
Payment of benefits expected in 2024	162,648
Payment of benefits expected in 2025 or after	2,432,602
Payment of benefits expected	R$ 3,112,980
Duration	11.88 years
G0 plan [member]
Summary of employee benefits [Line Items]
Payment of benefits expected in 2021	R$ 169,178
Payment of benefits expected in 2022	167,263
Payment of benefits expected in 2023	164,426
Payment of benefits expected in 2024	160,721
Payment of benefits expected in 2025 or after	1,887,953
Payment of benefits expected	R$ 2,549,541
Duration	9.40 years

The amount of expense from employee benefits (other than termination benefits), which are expected to be settled wholly within twelve months after the end of the annual reporting period in which the employees render the related services, that the entity does not separately disclose in the same statement or note. [Refer: Employee benefits expense]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2020-01-01
-Paragraph 9
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_9&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_OtherShorttermEmployeeBenefits
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The duration of payment of benefit expense.

+ References

No definition available.

+ Details

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

- Definition