v3.20.4
Share-Based Payments (Summary of Restricted Stock Unit Activity) (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Restricted Stock Units (RSUs)      
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount $ 233    
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition 2 years 4 months 24 days    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Beginning Balance 2.9    
Granted 0.9    
Converted (1.2)    
Forfeited (0.1)    
Outstanding at December 31, 2020 2.5 2.9  
Units vested and expected to vest at December 31, 2020 2.4    
Weighted-average grant-date fair value, units outstanding at January 1, 2020 $ 166    
Weighted-average grant-date fair value, granted 288 $ 226 $ 171
Weighted-average grant-date fair value, converted 116    
Weighted-average grant-date fair value, forfeited/expired 218    
Weighted-average grant-date fair value, units outstanding at December 31, 2020 231 $ 166  
Weighted-average grant-date fair value, units vested and expected to vest at December 31, 2020 $ 230    
Aggregate intrinsic value, units outstanding at December 31, 2020 $ 898    
Aggregate intrinsic value, units vested and expected to vest at December 31, 2020 $ 861    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 3 years    
Performance stock units      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Beginning Balance 0.5    
Granted 0.2    
Converted (0.3)    
Outstanding at December 31, 2020 0.4 0.5  
Units vested and expected to vest at December 31, 2020 0.4    
Weighted-average grant-date fair value, units outstanding at January 1, 2020 $ 167    
Weighted-average grant-date fair value, granted 291 $ 231 $ 226
Weighted-average grant-date fair value, converted 126    
Weighted-average grant-date fair value, units outstanding at December 31, 2020 259 $ 167  
Weighted-average grant-date fair value, units vested and expected to vest at December 31, 2020 $ 259    
Aggregate intrinsic value, units outstanding at December 31, 2020 $ 148    
Aggregate intrinsic value, units vested and expected to vest at December 31, 2020 $ 148    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 3 years    
Equity Option [Member]      
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount $ 37    
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition 2 years 1 month 6 days    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 4 years    
Minimum vesting from date of retirement eligibility | Performance stock units      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 7 months