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Share-based awards - Schedule of Weighted Average Fair Values and Assumptions Used (Details) - Employee Stock Option - $ / shares
6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average grant date fair value     $ 49.15 $ 42.43
Assumptions:        
Expected volatility     30.00% 30.00%
Dividend yield     0.00% 0.00%
Risk-free interest rate     0.78% 0.57%
Expected life 5 years 5 years