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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 |

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