Restructuring plans - Restructuring and Related Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		42 Months Ended
	Jul. 31, 2021	Aug. 01, 2020	Jul. 31, 2021	Aug. 01, 2020	Jul. 31, 2021
Restructuring Cost and Reserve [Line Items]
Total Signet Path to Brilliance Plan expenses	$ (0.9)	$ 28.9	$ (1.6)	$ 41.6
Cost of sales
Restructuring Cost and Reserve [Line Items]
Inventory charges			0.0	(0.6)
Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Other Plan related expenses			(1.6)	41.6
Signet Path to Brilliance
Restructuring Cost and Reserve [Line Items]
Total Signet Path to Brilliance Plan expenses	(0.9)	28.7	(1.6)	$ 41.0	$ 251.0
Signet Path to Brilliance | Cost of sales
Restructuring Cost and Reserve [Line Items]
Inventory charges	0.0	(0.2)
Signet Path to Brilliance | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Other Plan related expenses	(0.9)	$ 28.9
Inventory charges | Signet Path to Brilliance
Restructuring Cost and Reserve [Line Items]
Total Signet Path to Brilliance Plan expenses	0.0		0.0		72.8
Termination benefits | Signet Path to Brilliance
Restructuring Cost and Reserve [Line Items]
Total Signet Path to Brilliance Plan expenses	(0.4)		(1.1)		48.8
Store closure and other costs | Signet Path to Brilliance
Restructuring Cost and Reserve [Line Items]
Total Signet Path to Brilliance Plan expenses	$ (0.5)		$ (0.5)		$ 129.4