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Operating Costs And Expenses - Additional Information (Detail)
R$ in Millions, Employee in Millions
 1 Months Ended 12 Months Ended
Sep. 30, 2017
Apr. 30, 2017
Mar. 31, 2017
Dec. 31, 2017
BRL (R$)
Employee
Dec. 31, 2016
BRL (R$)
Disclosure Of Operating Costs And Expenses [Abstract]          
Period of eligibility for the severance program     25 years    
Employee voluntary severance program description       The period for acceptance of the 2017 PDVP was April 3 2017, through October 17, 2017.  
Payment of additional premium for employees joining in months   5 months      
Payment of premium for employees joining 1 month        
Penalty in percentage       40.00%  
Programmed voluntary retirement plan expense | R$       R$ 214 R$ 93
Number of employees completing severance | Employee       1,189