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Shareholders' equity - Additional Information (Detail) - USD ($) | 1 Months Ended |  |  |
--- | --- | --- | --- | ---
Aug. 31, 2016 | Oct. 28, 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 |  | $ 650,600,000 | $ 600,000,000 |

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