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Fair Value of Financial Instruments - Additional Information (Detail) - BRL (R$)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Standby letters of credit and financial guarantees R$ 76,852,000,000 R$ 79,703,000,000
Short-term assumption period 5 days  
Transfers out of Level 1 into Level 2 of fair value hierarchy, assets held at end of reporting period R$ 0  
Transfers out of Level 1 into Level 2 of fair value hierarchy, liabilities held at end of reporting period 0  
Transfers out of Level 2 into Level 1 of fair value hierarchy, assets held at end of reporting period 0  
Transfers out of Level 2 into Level 1 of fair value hierarchy, liabilities held at end of reporting period 0  
Transfers into Level 3 of fair value hierarchy, assets 0  
Transfers into Level 3 of fair value hierarchy, liabilities 0  
Transfers out of Level 3 of fair value hierarchy, assets 0  
Transfers out of Level 3 of fair value hierarchy, liabilities 0  
Fair vale of securities used to evaluate pricing service or brokers 22,231,000,000  
Level 2 [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Financial instruments classified as Level 2 52,849,000,000  
Estimated fair value [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Standby letters of credit and financial guarantees R$ 1,168,000,000 R$ 935,000,000
Bottom of range [member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Purchase price of securities, percentage 0.50%  
Top of range [member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Purchase price of securities, percentage 0.50%  
Scenarios I [Member] | Interest rate risk [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Shocks basis point 0.01%  
Scenarios I [Member] | Currency, commodities, and ratios [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Shocks basis point 5.00%  
Scenarios I [Member] | Bottom of range [member] | Nonlinear [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Shocks basis point 5.00%  
Scenarios I [Member] | Top of range [member] | Nonlinear [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Shocks basis point 25.00%  
Scenarios II [Member] | Interest rate risk [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Shocks basis point 0.25%  
Scenarios II [Member] | Currency, commodities, and ratios [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Shocks basis point 10.00%  
Scenarios II [Member] | Bottom of range [member] | Nonlinear [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Shocks basis point 10.00%  
Scenarios II [Member] | Top of range [member] | Nonlinear [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Shocks basis point 25.00%  
Scenarios III [Member] | Interest rate risk [Member]    
Disclosure of fair value measurement of assets and liabilities [Line Items]    
Shocks basis point 0.50%