Shareholders' equity - Share Repurchase (Details) - USD ($) $ / shares in Units, shares in Millions		9 Months Ended
	Oct. 05, 2016	Oct. 29, 2016	Oct. 31, 2015	Aug. 31, 2016	Feb. 29, 2016	Jun. 14, 2013
Class of Stock [Line Items]
Shares repurchased (shares)	4.7	9.9	0.9
Amount repurchased	$ 367,500,000	$ 842,500,000	$ 111,900,000
Average repurchase price per share (usd per share)		$ 85.00	$ 128.91
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
Average repurchase price per share (usd per share)		$ 111.26	$ 128.91
2016 Program
Class of Stock [Line Items]
Amount authorized		$ 1,375,000,000		$ 625,000,000	$ 750,000,000
Shares repurchased (shares)		8.7
Amount repurchased		$ 706,900,000
Average repurchase price per share (usd per share)		$ 81.32
Remaining authorized repurchase amount		$ 510,600,000