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Share-Based Compensation - Additional Information (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based compensation expense $ 40 $ 49 $ 130 $ 134  
Deferred compensation costs related to unvested awards $ 220   $ 220   $ 301
RSUs          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock awards, granted (in shares)     0.3    
Stock awards, vesting period     4 years    
Stock awards, period of service after grant date     1 year    
Stock awards, weighted average grant-date fair value (in USD per share)     $ 140    
PSUs          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock awards, granted (in shares)     0.2