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Interest and similar income and expense and net gain (loss) on investment securities and derivatives - Summary of Interest and Similar Expense (Detail) - BRL (R$) R$ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure Of Interest Expense [Line items] |  |  |
Interest and similar expense | R$ (70,612) | R$ (78,330) | R$ (95,129)
Bank Deposits [Member] |  |  |
Disclosure Of Interest Expense [Line items] |  |  |
Interest and similar expense | (17,484) | (13,340) | (14,701)
Securities sold under repurchase agreements [member] |  |  |
Disclosure Of Interest Expense [Line items] |  |  |
Interest and similar expense | (20,889) | (33,087) | (45,935)
Inter bank market debt [Member] |  |  |
Disclosure Of Interest Expense [Line items] |  |  |
Interest and similar expense | (13,587) | (10,059) | (8,347)
Institutional market debt [Member] |  |  |
Disclosure Of Interest Expense [Line items] |  |  |
Interest and similar expense | (6,773) | (6,852) | (8,249)
Finance Expense [Member] |  |  |
Disclosure Of Interest Expense [Line items] |  |  |
Interest and similar expense | (11,815) | (14,918) | (17,790)
Other interest and similar expense [Member] |  |  |
Disclosure Of Interest Expense [Line items] |  |  |
Interest and similar expense | R$ (64) | R$ (74) | R$ (107)

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