Pension plans - Components of Net Periodic Pension Cost (Details) - Foreign Pension Plan, Defined Benefit - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2015	Nov. 01, 2014	Oct. 31, 2015	Nov. 01, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ (0.7)	$ (0.6)	$ (2.0)	$ (1.8)
Interest cost	(1.9)	(2.4)	(5.8)	(7.4)
Expected return on UK Plan assets	2.9	3.7	8.7	11.2
Amortization of unrecognized net prior service credits	0.6	0.4	1.7	1.3
Amortization of unrecognized actuarial losses	(0.9)	(0.5)	(2.6)	(1.5)
Net periodic pension benefit	$ 0.0	$ 0.6	$ 0.0	$ 1.8