11 Related-Party Balances and Transactions (Details 1) - BRL (R$) R$ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of transactions between related parties [line items]
Revenues	R$ 17,797,541	R$ 17,983,654	R$ 16,085,094
Sanitation services [member]
Disclosure of transactions between related parties [line items]
Revenues	501,756	556,574	501,146
Payments received from related parties [member]
Disclosure of transactions between related parties [line items]
Revenues	(520,881)	(546,365)	(509,672)
Receipt of reimbursement referring to Law 4,819/58 [member]
Disclosure of transactions between related parties [line items]
Receipt of GESP reimbursement	R$ (173,874)	R$ (152,112)	R$ (173,516)

The income arising in the course of an entity's ordinary activities. Income is increases in assets, or decreases in liabilities, that result in increases in equity, other than those relating to contributions from holders of equity claims.

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+ Details