Pension plans - Components of Net Periodic Pension Cost (Details) - Foreign Pension Plan, Defined Benefit - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Aug. 01, 2015	Aug. 02, 2014	Aug. 01, 2015	Aug. 02, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ (0.7)	$ (0.6)	$ (1.3)	$ (1.2)
Interest cost	(2.0)	(2.5)	(3.9)	(5.0)
Expected return on UK Plan assets	3.0	3.7	5.8	7.5
Amortization of unrecognized net prior service credit	0.6	0.5	1.1	0.9
Amortization of unrecognized actuarial loss	(0.9)	(0.5)	(1.7)	(1.0)
Net periodic pension benefit	$ 0.0	$ 0.6	$ 0.0	$ 1.2