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10 Accounts Receivables - Concessions (Details 4) - Generation concession agreements [member] - BRL (R$)
R$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Accounts Receivable Concessions [Line Items]    
Power generation concession contract at beginning R$ 69,182 R$ 65,811
Gain on remeasurement of the cash flow 1,518 426
Reversal of impairment 10,502 2,945
Power generation concession contract at ending R$ 81,202 R$ 69,182