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Share-Based Compensation (Assumptions Used) (Details) - $ / shares
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Share-based Payment Arrangement [Abstract]    
Share price at grant (in dollars per share) $ 544.08 $ 288.78
Share price at exercise (in dollars per share) $ 548.15 $ 288.78
Expected stock price volatility 31.00% 27.00%
Expected term, in years 6 years 2 months 12 days 6 years
Risk-free interest rate 0.70% 1.50%
Weighted average fair value of options granted (in dollars per share) $ 168.35 $ 84.21