Other assets - Components of Other Assets (Details) - USD ($) $ in Millions	Apr. 29, 2017	Jan. 28, 2017	Apr. 30, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred ESP selling costs	$ 86.7	$ 86.1	$ 81.8
Investments	27.9	27.2	26.8
Other assets	50.5	51.8	48.6
Total other assets	165.1	165.1	157.2
Deferred costs related to the sale of the extended service plan	$ 29.6	$ 29.4	$ 27.5