Statements of Changes in Equity (Parenthetical) - R$ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of changes in equity [abstract]
Interest on shareholder's equity	R$ 0.33820	R$ 1.17012	R$ 0.9851
Additional proposed dividends, approved	R$ 0.11847	R$ 0.08827	R$ 0.07833

It is refers to the additional proposed dividends, approved.

No definition available.

Name:	sbs_AdditionalProposedDividendsApproved
Namespace Prefix:	sbs_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration