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Customers, Traders and Power Transport Concession Holders - Summary of Changes in Provision for Doubtful Accounts (Detail) - BRL (R$)
R$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Changes in allowance account for credit losses of financial assets [abstract]      
Beginning balance R$ 568 R$ 660 R$ 625
Effect of adoption of IFRS 9 on Jan. 1, 2018 (1) (Note 2.4) 150    
Additions, net 264 248 382
Disposals (231) (340) (347)
Ending balance R$ 751 R$ 568 R$ 660