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Stock-based Compensation (Narrative) (Details)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
director
$ / shares
shares
Dec. 31, 2019
USD ($)
$ / shares
Dec. 31, 2018
USD ($)
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Incentive stock option, exercise period, maximum, in years 10 years    
Maximum number of shares, options, SARs, or stock units granted or awarded in calendar year per participant 200,000    
Maximum aggregate number of shares of common stock that may be issued under the Plan 1,000,000    
Shares available for grant (in shares) 954,028    
Restricted Stock And Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock awards granted (in shares) 6,779    
Stock awards weighted average grant date fair value (in dollars per share) | $ / shares $ 414.33 $ 440.42 $ 415.98
Fair value of shares vested | $ $ 2 $ 1 $ 3
Compensation expense | $ 2 $ 2 $ 2
Unrecognized compensation expense | $ $ 5    
Period for recognition of unrecognized compensation expense, in years 3 years 1 month 6 days    
Non-Employee Directors [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock awards granted (in shares) 1,120    
Number of non-employee directors | director 5