Goodwill and intangibles - Summary of Goodwill (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jul. 29, 2017	Jan. 28, 2017
Goodwill [Roll Forward]
Beginning Balance	$ 517.6	$ 515.5
Impact of foreign exchange	2.3	2.1
Ending Balance	519.9	517.6
Sterling Jewelers
Goodwill [Roll Forward]
Beginning Balance	23.2	23.2
Impact of foreign exchange	0.0	0.0
Ending Balance	23.2	23.2
Zale Jewelry
Goodwill [Roll Forward]
Beginning Balance	490.8	488.7
Impact of foreign exchange	2.3	2.1
Ending Balance	493.1	490.8
Piercing Pagoda
Goodwill [Roll Forward]
Beginning Balance	0.0	0.0
Impact of foreign exchange	0.0	0.0
Ending Balance	0.0	0.0
UK Jewelry
Goodwill [Roll Forward]
Beginning Balance	0.0	0.0
Impact of foreign exchange	0.0	0.0
Ending Balance	0.0	0.0
Other
Goodwill [Roll Forward]
Beginning Balance	3.6	3.6
Impact of foreign exchange	0.0	0.0
Ending Balance	$ 3.6	$ 3.6