Other assets - Components of Other Assets (Detail) - USD ($) $ in Millions	Oct. 31, 2015	Jan. 31, 2015	Nov. 01, 2014
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred extended service plan selling costs	$ 74.6	$ 69.7	$ 64.8
Investments(1)	25.0	25.2	23.5
Other assets	44.9	45.1	45.2
Total other assets	144.5	140.0	133.5
Deferred costs related to the sale of the extended service plan	$ 24.0	$ 24.9	$ 23.1