Basis of presentation and accounting policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2014	Nov. 01, 2013	Oct. 31, 2014	Nov. 01, 2013	Jan. 30, 2015 period	Jan. 31, 2014 period
Basis of presentation
Fiscal year, number of weeks					52	52
LIFO provision (benefit)	$ 2.2	$ (3.7)	$ 3.1	$ (6.6)