Other assets - Components of Other Assets (Details) - USD ($) $ in Millions	Jul. 30, 2016	Jan. 30, 2016	Aug. 01, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred ESP selling costs	$ 82.6	$ 79.4	$ 75.2
Investments	27.0	26.8	23.2
Other assets	48.4	48.4	38.4
Total other assets	158.0	154.6	136.8
Deferred costs related to the sale of the extended service plan	$ 27.7	$ 26.4	$ 23.9