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Stock compensation plans - Weighted-average assumptions used to estimate fair value of options granted (Detail) - Stock Options
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Weighted Average Fair Values [Line Items]      
Risk-free interest rate 4.13% 1.56% 0.67%
Expected life of option 5 years 25 days 5 years 10 days 5 years 3 days
Expected dividend yield 0.57% 0.41% 0.34%
Expected volatility 31.42% 30.09% 30.03%