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Securities Sold Under Repurchase Agreements and Interbank and Institutional Market Debts - Summary of Breakdown of Funds Obtained in Institutional Markets (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Jan. 01, 2017
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Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | R$ 93,974 | R$ 98,482 | R$ 96,239
Subordinated debt [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | R$ 49,313 | 52,696 |
Subordinated debt [Member] | Bottom of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Interest rate for each operations | 3.80% |  |
Subordinated debt [Member] | Top of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Interest rate for each operations | 4.63% |  |
Foreign borrowing through securities [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | R$ 41,863 | 41,400 |
Foreign borrowing through securities [Member] | Bottom of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Interest rate for each operations | 0.89% |  |
Foreign borrowing through securities [Member] | Top of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Interest rate for each operations | 30.35% |  |
Structured Operations Certificates [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | R$ 2,798 | 4,386 |
Structured Operations Certificates [Member] | Bottom of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Interest rate for each operations | 0.00% |  |
Structured Operations Certificates [Member] | Top of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Interest rate for each operations | 15.82% |  |
Current [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | R$ 8,524 | 26,026 |
Current [Member] | Subordinated debt [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | 343 | 12,500 |
Current [Member] | Foreign borrowing through securities [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | 6,232 | 11,764 |
Current [Member] | Structured Operations Certificates [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | 1,949 | 1,762 |
Non-current [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | 85,450 | 72,456 |
Non-current [Member] | Subordinated debt [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | 48,970 | 40,196 |
Non-current [Member] | Foreign borrowing through securities [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | 35,631 | 29,636 |
Non-current [Member] | Structured Operations Certificates [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Institutional market debt | R$ 849 | R$ 2,624 |

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