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Financial Assets at Amortized Cost-Securities - Summary of Financial Assets at Amortized Cost - Securities (Detail) - BRL (R$) R$ in Millions | Dec. 31, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Jan. 01, 2017
--- | --- | --- | --- | ---
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | R$ 994,759 |  | R$ 905,729 | R$ 902,289
Brazilian government securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Fair Value |  | R$ 11,880 |  |
Financial assets securities [Member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 110,395 |  | 111,424 |
Expected loss | (3,646) |  | (5,182) |
Fair Value | 106,749 |  | 106,242 |
Financial assets securities [Member] | Brazilian government securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 54,064 |  | 54,875 |
Expected loss | (58) |  | (66) |
Fair Value | 54,006 |  | 54,809 |
Financial assets securities [Member] | Government securities - abroad [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 6,700 |  | 8,414 |
Expected loss | (3) |  | (3) |
Fair Value | 6,697 |  | 8,411 |
Financial assets securities [Member] | Government securities - abroad [member] | Colombia [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 356 |  | 836 |
Expected loss | (3) |  | (3) |
Fair Value | 353 |  | 833 |
Financial assets securities [Member] | Government securities - abroad [member] | Chile [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 256 |  | 154 |
Fair Value | 256 |  | 154 |
Financial assets securities [Member] | Government securities - abroad [member] | Korea [Member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 1,385 |  | 1,944 |
Fair Value | 1,385 |  | 1,944 |
Financial assets securities [Member] | Government securities - abroad [member] | Denmark [Member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost |  |  | 1,951 |
Fair Value |  |  | 1,951 |
Financial assets securities [Member] | Government securities - abroad [member] | Spain [Member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 2,411 |  | 2,937 |
Fair Value | 2,411 |  | 2,937 |
Financial assets securities [Member] | Government securities - abroad [member] | United States [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 19 |  | 16 |
Fair Value | 19 |  | 16 |
Financial assets securities [Member] | Government securities - abroad [member] | Mexico [Member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 2,258 |  | 559 |
Fair Value | 2,258 |  | 559 |
Financial assets securities [Member] | Government securities - abroad [member] | Paraguay [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost |  |  | 4 |
Fair Value | 0 |  | 4 |
Financial assets securities [Member] | Government securities - abroad [member] | Uruguay [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 15 |  | 13 |
Fair Value | 15 |  | 13 |
Financial assets securities [Member] | Corporate securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 49,631 |  | 48,135 |
Expected loss | (3,585) |  | (5,113) |
Fair Value | 46,046 |  | 43,022 |
Financial assets securities [Member] | Rural product note [Member] | Corporate securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 4,181 |  | 2,899 |
Expected loss | (178) |  | (160) |
Fair Value | 4,003 |  | 2,739 |
Financial assets securities [Member] | Bank deposit certificates [member] | Corporate securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 123 |  | 130 |
Fair Value | 123 |  | 130 |
Financial assets securities [Member] | Securitized real estate loans [Member] | Corporate securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 9,876 |  | 13,839 |
Expected loss | (361) |  | (2,056) |
Fair Value | 9,515 |  | 11,783 |
Financial assets securities [Member] | Debentures [member] | Corporate securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 29,001 |  | 23,397 |
Expected loss | (3,013) |  | (2,857) |
Fair Value | 25,988 |  | 20,540 |
Financial assets securities [Member] | Eurobonds and others [member] | Corporate securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 4,005 |  | 3,660 |
Expected loss | (2) |  | (3) |
Fair Value | 4,003 |  | 3,657 |
Financial assets securities [Member] | Financial bills [Member] | Corporate securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost |  |  | 60 |
Fair Value |  |  | 60 |
Financial assets securities [Member] | Promissory notes [Member] | Corporate securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 1,069 |  | 3,246 |
Expected loss | (14) |  | (23) |
Fair Value | 1,055 |  | 3,223 |
Financial assets securities [Member] | Other [member] | Corporate securities [member] |  |  |  |
Disclosure of Financial Assets [Line Items] |  |  |  |
Amortized cost | 1,376 |  | 904 |
Expected loss | (17) |  | (14) |
Fair Value | R$ 1,359 |  | R$ 890 |

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