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10 Accounts Receivables - Concessions (Details 3) - Bonus from the grant of concession agreements under the quota system [member] - BRL (R$)
R$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Accounts Receivable Concessions [Line Items]    
Bonus from the grant, beginning R$ 647,984 R$ 625,772
Transfers to electricity grid use charges - customers (71,087) (69,192)
Interest 94,307 91,404
Bonus from the grant, ending R$ 671,204 R$ 647,984