Shareholders' equity - Additional Information (Detail) - USD ($)	Jul. 30, 2016	Feb. 29, 2016	Jun. 14, 2013
2016 Program
Class of Stock [Line Items]
Amount authorized		$ 750,000,000
Remaining authorized repurchase amount	$ 510,600,000
2013 Program
Class of Stock [Line Items]
Amount authorized			$ 350,000,000