Goodwill and intangibles - Summary of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended
	May 05, 2018	Apr. 29, 2017
Goodwill [Roll Forward]
Beginning Balance	$ 821.7	$ 517.6
Acquisitions		301.7
Impairment	(308.8)
Impact of foreign exchange and other adjustments	(3.8)	2.4
Ending Balance	509.1	516.1
Intangible assets, purchase accounting adjustments	2.6
North America
Goodwill [Roll Forward]
Beginning Balance	818.1	514.0
Acquisitions		301.7
Impairment	(308.8)
Impact of foreign exchange and other adjustments	(3.8)	2.4
Ending Balance	505.5
Other
Goodwill [Roll Forward]
Beginning Balance	3.6	3.6
Acquisitions		0.0
Impairment	0.0
Impact of foreign exchange and other adjustments	0.0	$ 0.0
Ending Balance	$ 3.6