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Shareholders' equity - Summary of Weighted Average Number of Shares Per Share (Detail) - shares
shares in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Earnings per share [line items]        
Basic and Diluted 73.5 73.0 73.2 72.8