Other assets - Components of Other Assets (Details) - USD ($) $ in Millions	Oct. 28, 2017	Jan. 28, 2017	Oct. 29, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred ESP selling costs	$ 86.0	$ 86.1	$ 81.8
Investments	28.7	27.2	27.5
Other assets	54.4	51.8	48.2
Total other assets	169.1	165.1	157.5
Deferred costs related to the sale of the extended service plan	$ 29.3	$ 29.4	$ 27.6