Earnings per share - Schedule of Earnings per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Aug. 01, 2015	Aug. 02, 2014	Aug. 01, 2015	Aug. 02, 2014
Equity [Abstract]
Net income	$ 62.2	$ 58.0	$ 181.0	$ 154.6
Basic weighted average number of shares outstanding (shares)	79.7	79.9	79.8	79.9
Dilutive effect of share awards (shares)	0.2	0.3	0.2	0.3
Diluted weighted average number of shares outstanding (shares)	79.9	80.2	80.0	80.2
Earnings per share - basic (usd per share)	$ 0.78	$ 0.73	$ 2.27	$ 1.93
Earnings per share - diluted (usd per share)	$ 0.78	$ 0.72	$ 2.26	$ 1.93