Shareholders' equity - Share Repurchase (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended
	May 04, 2019	May 05, 2018
Class of Stock [Line Items]
Shares repurchased (shares)	0.0	1.5
Amount repurchased	$ 0	$ 60,000,000
Average repurchase price per share (usd per share)	$ 0.00	$ 39.62
2017 Program
Class of Stock [Line Items]
Amount authorized	$ 600,000,000
Shares repurchased (shares)	0.0	0.2
Amount repurchased	$ 0	$ 9,400,000
Average repurchase price per share (usd per share)	$ 0.00	$ 38.86
Remaining authorized repurchase amount	$ 165,600,000
2016 Program
Class of Stock [Line Items]
Amount authorized	$ 1,375,000,000
Shares repurchased (shares)		1.3
Amount repurchased		$ 50,600,000
Average repurchase price per share (usd per share)		$ 39.76