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Risk and Capital Management - Summary of Position of Accounts Subject to Currency Risk (Detail) - Foreign exchange risk [member] - BRL (R$)
R$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Disclosure of position of accounts subject to currency risk [Line Items]    
Net exposure of financial instruments R$ (15,125) R$ 4,481
United States of America, Dollars    
Disclosure of position of accounts subject to currency risk [Line Items]    
Net exposure of financial instruments (38,190) (15,910)
Chile, Pesos    
Disclosure of position of accounts subject to currency risk [Line Items]    
Net exposure of financial instruments 7,647 7,159
Other [Member]    
Disclosure of position of accounts subject to currency risk [Line Items]    
Net exposure of financial instruments R$ 15,418 R$ 13,232