Shareholders' equity - Additional Information (Detail) - USD ($) shares in Millions		3 Months Ended		9 Months Ended
	Oct. 05, 2016	Oct. 29, 2016	Oct. 31, 2015	Oct. 29, 2016	Oct. 31, 2015	Aug. 31, 2016	Feb. 29, 2016	Jun. 14, 2013
Class of Stock [Line Items]
Accelerated share repurchases, payment	$ 525,000,000	$ 525,000,000		$ 525,000,000
Shares repurchased (shares)	4.7			9.9	0.9
Amount repurchased	$ 367,500,000			$ 842,500,000	$ 111,900,000
Dividends on preferred shares		18,100,000	$ 17,500,000	18,100,000	17,500,000
Dividends on redeemable convertible preferred shares		2,200,000	$ 0	2,200,000	$ 0
2016 Program
Class of Stock [Line Items]
Amount authorized		1,375,000,000		$ 1,375,000,000		$ 625,000,000	$ 750,000,000
Shares repurchased (shares)				8.7
Amount repurchased				$ 706,900,000
2013 Program
Class of Stock [Line Items]
Amount authorized								$ 350,000,000
Shares repurchased (shares)				1.2	0.9
Amount repurchased				$ 135,600,000	$ 111,900,000
Common shares
Class of Stock [Line Items]
Shares repurchased (shares)				5.2
Amount repurchased				$ 475,000,000
Series A Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Dividends on preferred shares		$ 0		$ 0