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Shareholders' equity - Additional Information (Detail) - USD ($)
1 Months Ended
Aug. 31, 2016
Jul. 29, 2017
Jun. 30, 2017
Feb. 29, 2016
2016 Program        
Class of Stock [Line Items]        
Amount authorized $ 1,375,000,000 $ 1,375,000,000   $ 750,000,000
Increase in authorized share repurchase program amount $ 625,000,000      
2017 Program        
Class of Stock [Line Items]        
Amount authorized     $ 600,000,000