Earnings per share - Schedule of Earnings per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2015	Nov. 01, 2014	Oct. 31, 2015	Nov. 01, 2014
Equity [Abstract]
Net income (loss)	$ 15.0	$ (1.3)	$ 196.0	$ 153.3
Basic weighted average number of shares outstanding (shares)	79.3	79.9	79.7	79.9
Dilutive effect of share awards (shares)	0.2	0.0	0.2	0.3
Diluted weighted average number of shares outstanding (shares)	79.5	79.9	79.9	80.2
Earnings (loss) per share - basic (usd per share)	$ 0.19	$ (0.02)	$ 2.46	$ 1.92
Earnings (loss) per share - diluted (usd per share)	$ 0.19	$ (0.02)	$ 2.45	$ 1.91