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Securities Sold Under Repurchase Agreements and Interbank and Institutional Market Debts - Summary of Securities Sold Under Repurchase Agreements (Detail) - BRL (R$) R$ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Jan. 01, 2017
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | R$ 330,237 | R$ 312,634 | R$ 349,164
Assets Pledged as Collateral [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 77,651 | 109,253 |
Assets Pledged as Collateral [member] | Government securities - abroad [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 46,680 | 43,491 |
Assets Pledged as Collateral [member] | Corporate securities [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 9,051 | 6,564 |
Assets Pledged as Collateral [member] | Own issue [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 21,417 | 58,837 |
Assets Pledged as Collateral [member] | Foreign securities [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | R$ 503 | 361 |
Assets Pledged as Collateral [member] | Bottom of range [member] | Government securities - abroad [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 93.50% |  |
Assets Pledged as Collateral [member] | Bottom of range [member] | Corporate securities [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 40.00% |  |
Assets Pledged as Collateral [member] | Bottom of range [member] | Own issue [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 65.00% |  |
Assets Pledged as Collateral [member] | Bottom of range [member] | Foreign securities [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 0.22% |  |
Assets Pledged as Collateral [member] | Top of range [member] | Government securities - abroad [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 6.40% |  |
Assets Pledged as Collateral [member] | Top of range [member] | Corporate securities [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 97.70% |  |
Assets Pledged as Collateral [member] | Top of range [member] | Own issue [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 16.93% |  |
Assets Pledged as Collateral [member] | Top of range [member] | Foreign securities [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 5.20% |  |
Assets Received as Collateral [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | R$ 172,953 | 146,853 |
Assets Received as Collateral [member] | Bottom of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 5.60% |  |
Assets Received as Collateral [member] | Top of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 6.40% |  |
Right to sell or repledge collateral [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | R$ 79,633 | 56,528 |
Right to sell or repledge collateral [member] | Bottom of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 97.50% |  |
Right to sell or repledge collateral [member] | Top of range [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Percentage of securities sold under repurchase agreements | 10.00% |  |
Current [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | R$ 271,521 | 240,808 |
Current [Member] | Assets Pledged as Collateral [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 71,231 | 82,075 |
Current [Member] | Assets Pledged as Collateral [member] | Government securities - abroad [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 46,676 | 43,491 |
Current [Member] | Assets Pledged as Collateral [member] | Corporate securities [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 9,051 | 6,564 |
Current [Member] | Assets Pledged as Collateral [member] | Own issue [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 15,156 | 31,659 |
Current [Member] | Assets Pledged as Collateral [member] | Foreign securities [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 348 | 361 |
Current [Member] | Assets Received as Collateral [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 172,953 | 146,853 |
Current [Member] | Right to sell or repledge collateral [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 27,337 | 11,880 |
Non-current [Member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 58,716 | 71,826 |
Non-current [Member] | Assets Pledged as Collateral [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 6,420 | 27,178 |
Non-current [Member] | Assets Pledged as Collateral [member] | Government securities - abroad [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 4 |  |
Non-current [Member] | Assets Pledged as Collateral [member] | Own issue [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 6,261 | 27,178 |
Non-current [Member] | Assets Pledged as Collateral [member] | Foreign securities [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | 155 |  |
Non-current [Member] | Right to sell or repledge collateral [member] |  |  |
Disclosure Of Repurchase Agreements [Line Items] |  |  |
Securities sold under repurchase agreements | R$ 52,296 | R$ 44,648 |

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