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Risk and Capital Management - Summary of Financial Assets Individually Evaluated Classified by Rating (Detail) - BRL (R$) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 752,920,000,000 | R$ 705,674,000,000
Other financial assets, individually evaluated, classified by rating, percentage | 100.00% | 100.00%
Lower risk [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 743,932,000,000 | R$ 702,365,000,000
Satisfactory [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | 4,985,000,000 | 1,616,000,000
Higher Risk [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | 4,003,000,000 | 1,693,000,000
Interbank deposits and securities purchased under agreements to resell [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 306,556,000,000 | R$ 273,747,000,000
Other financial assets, individually evaluated, classified by rating, percentage | 40.60% | 38.70%
Interbank deposits and securities purchased under agreements to resell [Member] | Lower risk [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 306,556,000,000 | R$ 273,747,000,000
Financial assets at fair value through profit or loss [member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 110,395,000,000 | R$ 106,242,000,000
Other financial assets, individually evaluated, classified by rating, percentage | 14.70% | 15.10%
Financial assets at fair value through profit or loss [member] | Lower risk [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 103,157,000,000 | R$ 104,610,000,000
Financial assets at fair value through profit or loss [member] | Satisfactory [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | 3,645,000,000 | 338,000,000
Financial assets at fair value through profit or loss [member] | Higher Risk [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | 3,593,000,000 | 1,294,000,000
Financial assets designated at fair value through profit or loss [member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 286,646,000,000 | R$ 273,536,000,000
Other financial assets, individually evaluated, classified by rating, percentage | 38.10% | 38.80%
Financial assets designated at fair value through profit or loss [member] | Lower risk [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 284,896,000,000 | R$ 271,859,000,000
Financial assets designated at fair value through profit or loss [member] | Satisfactory [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | 1,340,000,000 | 1,278,000,000
Financial assets designated at fair value through profit or loss [member] | Higher Risk [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | 410,000,000 | 399,000,000
Available-for-sale financial assets [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 49,323,000,000 | R$ 52,149,000,000
Other financial assets, individually evaluated, classified by rating, percentage | 6.60% | 7.40%
Available-for-sale financial assets [Member] | Lower risk [Member] |  |
Disclosure of financial assets individually evaluated classified by rating [Line Items] |  |
Other financial assets, individually evaluated, classified by rating | R$ 49,323,000,000 | R$ 52,149,000,000

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