Warranty reserve (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 29, 2016	Oct. 31, 2015	Oct. 29, 2016	Oct. 31, 2015
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at beginning of period	$ 40.4	$ 43.1	$ 41.9	$ 44.9
Warranty expense	3.7	3.0	9.4	7.9
Utilized	(3.6)	(3.6)	(10.8)	(10.3)
Balance at end of period	$ 40.5	$ 42.5	$ 40.5	$ 42.5