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Financial Assets at Amortized Cost-Securities - Summary of Financial Assets at Amortized Cost - Securities (Parenthetical) (Detail) - BRL (R$) R$ in Millions | Jun. 30, 2018 | Dec. 31, 2018 | Dec. 31, 2017
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Disclosure of Financial Assets [Line Items] |  |  |
Securities Pledged as Collateral of Funding Transactions of Financial Institutions and Clients |  | R$ 33,848 | R$ 27,469
Brazilian government securities [member] |  |  |
Disclosure of Financial Assets [Line Items] |  |  |
Securities Pledged as Collateral of Funding Transactions of Financial Institutions and Clients |  | 24,988 | 26,953
Classification of Debt Securities from Fair Value Through Profit or Loss to amortized cost | R$ 3,707 |  |
Classification of Debt Securities from Fair Value Through Other Comprehensive Income to amortized cost | 8,678 |  |
Debt securities at fair value | 11,880 |  |
Reclassification adjustment of debt securities at fair value | R$ (282) |  |
Government securities - abroad [member] |  |  |
Disclosure of Financial Assets [Line Items] |  |  |
Securities Pledged as Collateral of Funding Transactions of Financial Institutions and Clients |  |  | 479
Corporate securities [member] |  |  |
Disclosure of Financial Assets [Line Items] |  |  |
Securities Pledged as Collateral of Funding Transactions of Financial Institutions and Clients |  | R$ 8,860 | R$ 37

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