Shareholders' equity - Share Repurchase (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Nov. 03, 2018	Oct. 28, 2017
Class of Stock [Line Items]
Shares repurchased (shares)	8.8	8.1
Amount repurchased	$ 485.0	$ 460.0
Average repurchase price per share (usd per share)	$ 55.06	$ 56.91
2017 Program
Class of Stock [Line Items]
Amount authorized	$ 600.0
Shares repurchased (shares)	7.5
Amount repurchased	$ 434.4
Average repurchase price per share (usd per share)	$ 57.64
2016 Program
Class of Stock [Line Items]
Amount authorized	$ 1,375.0
Shares repurchased (shares)	1.3	8.1
Amount repurchased	$ 50.6	$ 460.0
Average repurchase price per share (usd per share)	$ 39.76	$ 56.91
Remaining authorized repurchase amount	$ 165.6