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Concession Financial and Sector Assets and Liabilities - Summary of Generation Indemnity Receivable (Parenthetical) (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Financial Assets and Liabilities Of The Concession [line items]        
Investments   R$ 7,792 R$ 8,694 R$ 9,717
Inflation adjustment, net of transfer R$ 323      
Miranda hydroelectric plant [member]        
Disclosure Of Financial Assets and Liabilities Of The Concession [line items]        
Investments 23      
Sao simao hydroelectric plant [member]        
Disclosure Of Financial Assets and Liabilities Of The Concession [line items]        
Investments 3      
Jaguara hydroelectric plant [member]        
Disclosure Of Financial Assets and Liabilities Of The Concession [line items]        
Investments R$ 174