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Investments in Associates and Joint Ventures - Summary of Main Investments (Parenthetical) (Detail) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 49.90% |
Percentage interest in voting capital | 30.06% |
Porto Seguro Itau Unibanco Participacoes S.A. [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 42.93% | 42.93%
Percentage interest in voting capital | 42.93% | 42.93%
BSF Holding S.A. [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 49.00% | 49.00%
Percentage interest in voting capital | 49.00% | 49.00%
IRB-Brasil Resseguros S.A. [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 11.20% | 11.20%
Percentage interest in voting capital | 11.20% | 11.20%
Gestora De Inteligencia De Credito S A [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 20.00% | 20.00%
Percentage interest in voting capital | 20.00% | 20.00%
Compania Uruguaya De Medios De Procesamiento S A [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 35.83% | 35.83%
Percentage interest in voting capital | 35.83% | 35.83%
Rias Redbanc S A [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 25.00% | 25.00%
Percentage interest in voting capital | 25.00% | 25.00%
Kinea Private Equity Investimentos S A [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 80.00% | 80.00%
Percentage interest in voting capital | 40.00% | 49.00%
Tecnologia Bancaria S A [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 28.95% | 28.95%
Percentage interest in voting capital | 28.95% | 28.95%
Olimpia Promocao e Servicos S.A. [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 50.00% | 50.00%
Percentage interest in voting capital | 50.00% | 50.00%
Conectcar Solucoes de Mobilidade Eletronica S.A. [Member] |  |
Disclosure of investments in associates and joint ventures [Line Items] |  |
Percentage interest in total capital | 50.00% | 50.00%
Percentage interest in voting capital | 50.00% | 50.00%

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