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Stockholders' Equity - Summary of Common Stock (Detail) - shares
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Series A [Member]    
Disclosure of Classes of Share Capital [Line Items]    
Subscribed and paid shares 29,457,941,452 30,214,262,692
Unissued shares authorized for executives' stock compensation programs 881,442,830 881,442,830
Repurchased shares 756,323,120 315,400,000
Shares that guarantee/guaranteed the issuance of convertible securities 1,970,862,596 2,842,339,760
Shares authorized for the issuance of stock or convertible securities 302,144,720 302,144,720
Number of shares issued 33,368,714,718 34,555,590,002
Series B [Member]    
Disclosure of Classes of Share Capital [Line Items]    
Subscribed and paid shares 14,728,970,726 15,107,131,346
Unissued shares authorized for executives' stock compensation programs 440,721,415 440,721,415
Repurchased shares 378,161,560 157,700,000
Shares that guarantee/guaranteed the issuance of convertible securities 985,431,298 1,421,169,880
Shares authorized for the issuance of stock or convertible securities 151,072,360 151,072,360
Number of shares issued 16,684,357,359 17,277,795,001