Accumulated other comprehensive income (loss) - Reclassifications out of AOCI (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jul. 29, 2017	Jul. 30, 2016	Jul. 29, 2017	Jul. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales reclassification adjustment		$ 941.7	$ 908.5	$ 1,853.9	$ 1,887.0
Interest expense reclassification adjustment		13.5	11.9	26.1	23.7
Income before income taxes		(122.1)	(108.0)	(224.8)	(308.2)
Income taxes		28.7	26.1	52.9	79.5
Net income		(93.4)	(81.9)	(171.9)	(228.7)
Amounts reclassified from AOCI		(0.9)	0.5	(2.0)	1.5
Gains (losses) on cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes		(1.4)	1.0	(3.3)	2.6
Income taxes		0.3	(0.4)	0.8	(0.9)
Net income		(1.1)	0.6	(2.5)	1.7
Gains (losses) on cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income | Foreign currency contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales reclassification adjustment		(1.2)	(0.4)	(2.2)	(0.6)
Gains (losses) on cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income | Interest rate swaps
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest expense reclassification adjustment		0.1	0.6	0.4	1.2
Gains (losses) on cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income | Commodity contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales reclassification adjustment		(0.3)	0.8	(1.5)	2.0
Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment from AOCI, pension and other postretirement benefit plans, before tax	[1]	0.8	0.4	1.5	0.8
Prior service credits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment from AOCI, pension and other postretirement benefit plans, before tax	[1]	(0.5)	(0.5)	(0.9)	(1.0)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment from AOCI, pension and other postretirement benefit plans, before tax		0.3	(0.1)	0.6	(0.2)
Reclassification adjustment from AOCI, pension and other postretirement benefit plans, tax		(0.1)	0.0	(0.1)	0.0
Amounts reclassified from AOCI		$ 0.2	$ (0.1)	$ 0.5	$ (0.2)

[1] These items are included in the computation of net periodic pension benefit.