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Income and Social Contribution Taxes - Summary of Estimated Balance of Deferred Tax Asset (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure Of Future Taxable Profits Enable Deferred Tax Assets [Line Items] |  |
Deferred tax assets future taxable profits | R$ 3,052 | R$ 2,953
2018 [member] |  |
Disclosure Of Future Taxable Profits Enable Deferred Tax Assets [Line Items] |  |
Deferred tax assets future taxable profits | 421 |
2019 [member] |  |
Disclosure Of Future Taxable Profits Enable Deferred Tax Assets [Line Items] |  |
Deferred tax assets future taxable profits | 477 |
2020 [member] |  |
Disclosure Of Future Taxable Profits Enable Deferred Tax Assets [Line Items] |  |
Deferred tax assets future taxable profits | 476 |
2021 [member] |  |
Disclosure Of Future Taxable Profits Enable Deferred Tax Assets [Line Items] |  |
Deferred tax assets future taxable profits | 452 |
2022 [member] |  |
Disclosure Of Future Taxable Profits Enable Deferred Tax Assets [Line Items] |  |
Deferred tax assets future taxable profits | 465 |
2022-2024 [member] |  |
Disclosure Of Future Taxable Profits Enable Deferred Tax Assets [Line Items] |  |
Deferred tax assets future taxable profits | 493 |
2025-2026 [Member] |  |
Disclosure Of Future Taxable Profits Enable Deferred Tax Assets [Line Items] |  |
Deferred tax assets future taxable profits | R$ 268 |

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