Shareholders' equity - Share Repurchase (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended
	Apr. 29, 2017	Apr. 30, 2016	Aug. 31, 2016	Feb. 29, 2016
Class of Stock [Line Items]
Shares repurchased (shares)	0.0	1.1
Amount repurchased	$ 0	$ 125,000,000
Average repurchase price per share (usd per share)	$ 0.00	$ 111.45
2016 Program
Class of Stock [Line Items]
Amount authorized	$ 1,375,000,000		$ 1,375,000,000	$ 750,000,000
Shares repurchased (shares)	0.0	0.0
Amount repurchased	$ 0	$ 0
Average repurchase price per share (usd per share)	$ 0.00	$ 0.00
Remaining authorized repurchase amount	$ 510,600,000
2013 Program
Class of Stock [Line Items]
Amount authorized		$ 350,000,000
Shares repurchased (shares)		1.1
Amount repurchased		$ 125,000,000
Average repurchase price per share (usd per share)		$ 111.45