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Operating Costs And Expenses - Additional Information (Detail)
R$ in Millions
 1 Months Ended 3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2019
BRL (R$)
Employee
Dec. 31, 2018
BRL (R$)
Employee
Dec. 31, 2017
BRL (R$)
Employee
Dec. 31, 2016
BRL (R$)
Disclosure of operating costs and expenses [line Items]          
Period of eligibility for the severance program 25 years   25 years    
Penalty in percentage     40.00%    
Programmed voluntary retirement plan expense | R$     R$ 26 R$ 214 R$ 93
Number of employees completing severance | Employee     151 1,189  
PDVP 2019 [member]          
Disclosure of operating costs and expenses [line Items]          
Programmed voluntary retirement plan expense | R$   R$ 21 R$ 66    
Number of employees completing severance | Employee   155 458