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Fair Value of Financial Instruments - Additional Information (Detail)
R$ in Millions
 12 Months Ended
Dec. 31, 2019
USD ($)
Dec. 31, 2019
BRL (R$)
Dec. 31, 2018
BRL (R$)
Disclosure of fair value measurement of assets and liabilities [Line Items]      
Standby letters of credit and financial guarantees | R$   R$ 81,733 R$ 76,852
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 $ 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 | R$   8,812  
Level 2 [Member]      
Disclosure of fair value measurement of assets and liabilities [Line Items]      
Financial instruments classified as Level 2 | R$   48,110  
Estimated fair value [member]      
Disclosure of fair value measurement of assets and liabilities [Line Items]      
Standby letters of credit and financial guarantees | R$   R$ 968 R$ 1,168
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 1.00%    
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 25.00%    
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 50.00%