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Stockholders' Equity - Summary of Appropriated Reserves (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Jan. 01, 2017 | Dec. 31, 2016
--- | --- | --- | --- | ---
Disclosure of reserves within equity [line items] |  |  |  |
Capital reserves | R$ 285 | R$ 285 |  | R$ 285
Revenue reserves | 13,195 | 12,214 |  | 3,158
Total reserves at parent company | 13,480 | 12,499 | R$ 3,443 | 3,443
Premium on subscription of shares [Member] |  |  |  |
Disclosure of reserves within equity [line items] |  |  |  |
Capital reserves | 284 | 284 |  | 284
Reserves from tax incentives, restatement of equity securities and other [Member] |  |  |  |
Disclosure of reserves within equity [line items] |  |  |  |
Capital reserves | 1 | 1 |  | 1
Legal [Member] |  |  |  |
Disclosure of reserves within equity [line items] |  |  |  |
Revenue reserves | 9,989 | 8,892 |  | 7,838
Statutory [Member] |  |  |  |
Disclosure of reserves within equity [line items] |  |  |  |
Revenue reserves | (2,775) | 589 |  | 1,132
Corporate reorganizations [member] |  |  |  |
Disclosure of reserves within equity [line items] |  |  |  |
Revenue reserves | (11,517) | (10,925) |  | (10,862)
Special revenue reserves [member] |  |  |  |
Disclosure of reserves within equity [line items] |  |  |  |
Revenue reserves | R$ 17,498 | R$ 13,658 |  | R$ 5,050

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