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Share-based Payments - Summary of Black-Scholes Option-Pricing Models (Details) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure Of Share Based Payments [Line Items]      
Weighted-average share price (US$) $ 162.82 $ 136.09 $ 142.20
Bottom of Range      
Disclosure Of Share Based Payments [Line Items]      
Expected volatility (%) 30.00% 30.10% 32.00%
Risk-free interest rate (%) 0.10% 1.40% 2.40%
Expected life of stock options (years) 2 years 7 months 6 days 2 years 6 months 2 years 4 months 24 days
Top of Range      
Disclosure Of Share Based Payments [Line Items]      
Expected volatility (%) 42.80% 35.20% 34.70%
Risk-free interest rate (%) 1.70% 2.60% 2.90%
Expected life of stock options (years) 4 years 9 months 18 days 4 years 9 months 18 days 4 years 4 months 24 days