v3.20.4
Employee Incentive Plans - Schedule of Restricted Stock Units, Vested and Expected to Vest (Parenthetical) (Detail) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock units granted, Weighted average grant-date fair value $ 220.45 $ 177.42 $ 218.06
Share-based Compensation, Liquidity discount RSUs 10.10% 10.50% 11.90%
Restricted stock units, post-vesting transfer restrictions period 4 years    
Share-based compensation arrangement by Share-based payment award, Equity instruments other than options, Vested in period, Total fair value $ 2,010 $ 2,000 $ 1,790
Restricted stock subject to future service 72,369 23,068  
No Future Service Required [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
RSUs outstanding 15,223,219 14,698,855  
RSUs subject to performance conditions [Member] | No Future Service Required [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
RSUs outstanding 489,602 268,433  
RSUs subject to performance conditions [Member] | No Future Service Required [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
RSUs outstanding 734,403 402,650  
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
RSUs outstanding 210,692 224,898