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Stockholders' equity - Additional Information (Detail) - R$ / shares
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of classes of share capital [line items]      
Total share capital 9,804,135,348 9,804,135,348 6,550,514,438
Number of common stock 4,958,290,359    
Number of preferred stock 4,845,844,989    
Cancellation of Shares 14,424,206 14,424,206  
Percentage of stock split approved 50    
Annual minimum priority dividend R$ 0.015    
Bottom of range [member]      
Disclosure of classes of share capital [line items]      
Annual mandatory dividend rate 25.00%    
Preference shares [member]      
Disclosure of classes of share capital [line items]      
Total share capital 4,845,844,989 4,845,844,989 3,230,563,326
Annual minimum priority dividend R$ 0.022