Revenue recognition - Narrative (Details) - North America	3 Months Ended
	May 05, 2018
Extended Service Plans and Lifetime Warranty Agreements
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, expected timing of satisfaction, period	17 years
Jewelry Replacement Plan
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, expected timing of satisfaction, period	3 years