Fair value measurements - Fair Value of Assets and Liabilities (Details) - USD ($) $ in Millions	Apr. 29, 2017	Jan. 28, 2017	Apr. 30, 2016
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 11.9	$ 11.9	$ 12.2
Liabilities	0.0	0.0	0.0
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	19.2	18.9	20.5
Liabilities	(1.3)	(3.6)	(3.8)
US Treasury securities | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	7.9	8.1	8.8
US Treasury securities | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0	0.0
Corporate equity securities | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	4.0	3.8	3.4
Corporate equity securities | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0	0.0
Foreign currency contracts | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0	0.0
Liabilities	0.0	0.0	0.0
Foreign currency contracts | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.4	3.2	0.4
Liabilities	(1.3)	(0.2)	(0.6)
Commodity contracts | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0	0.0
Liabilities	0.0	0.0	0.0
Commodity contracts | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	2.0	0.0	5.5
Liabilities	0.0	(3.4)	0.0
Interest rate swaps | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		0.0	0.0
Liabilities	0.0	0.0	0.0
Interest rate swaps | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.8	0.4	0.0
Liabilities	0.0	0.0	(3.2)
US government agency securities | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0	0.0
US government agency securities | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	4.9	4.4	3.3
Corporate bonds and notes | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0	0.0
Corporate bonds and notes | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	11.1	10.9	11.3
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	31.1	30.8	32.7
Liabilities	(1.3)	(3.6)	(3.8)
Carrying Value | US Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	7.9	8.1	8.8
Carrying Value | Corporate equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	4.0	3.8	3.4
Carrying Value | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.4	3.2	0.4
Liabilities	(1.3)	(0.2)	(0.6)
Carrying Value | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	2.0	0.0	5.5
Liabilities	0.0	(3.4)	0.0
Carrying Value | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.8	0.4	0.0
Liabilities	0.0	0.0	(3.2)
Carrying Value | US government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	4.9	4.4	3.3
Carrying Value | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 11.1	$ 10.9	$ 11.3