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Financial Assets at Fair Value Through Other Comprehensive Income-Securities - Summary of Fair Value and Corresponding Gross Carrying Amount of Financial Assets at Fair Value Through Other Comprehensive Income-Securities Assets (Parenthetical) (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Disclosure of fair value of investments in equity instruments designated at fair value through other comprehensive income [line items] |  |
Financial assets at fair value through other comprehensive income-Securities pledged in guarantee of funding transactions of financial institutions and clients | R$ 28,967 | R$ 27,469
Brazilian government securities [member] |  |
Disclosure of fair value of investments in equity instruments designated at fair value through other comprehensive income [line items] |  |
Financial assets at fair value through other comprehensive income-Securities pledged in guarantee of funding transactions of financial institutions and clients | 25,147 | 26,953
Government securities - abroad [member] |  |
Disclosure of fair value of investments in equity instruments designated at fair value through other comprehensive income [line items] |  |
Financial assets at fair value through other comprehensive income-Securities pledged in guarantee of funding transactions of financial institutions and clients | 3,583 | 37
Corporate securities [member] |  |
Disclosure of fair value of investments in equity instruments designated at fair value through other comprehensive income [line items] |  |
Financial assets at fair value through other comprehensive income-Securities pledged in guarantee of funding transactions of financial institutions and clients | R$ 237 | R$ 479

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