Revenue recognition - Narrative (Details)	Nov. 03, 2018	Feb. 03, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue recognized, percentage	55.00%	58.00%
Extended Service Plans and Lifetime Warranty Agreements | North America
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, expected timing of satisfaction, period	17 years
Jewelry Replacement Plan | North America
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, expected timing of satisfaction, period	3 years