Pension plans - Components of Net Periodic Pension Cost (Details) (Foreign Pension Plan, Defined Benefit, USD $) In Millions, unless otherwise specified	3 Months Ended
	May 02, 2015	May 03, 2014
Foreign Pension Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ (0.6)	$ (0.6)
Interest cost	(1.9)	(2.5)
Expected return on UK Plan assets	2.8	3.8
Amortization of unrecognized net prior service credit	0.5	0.4
Amortization of unrecognized actuarial loss	(0.8)	(0.5)
Net periodic pension benefit	$ 0	$ 0.6