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Restructuring plans - Restructuring and Related Costs (Details) - USD ($) $ in Millions	12 Months Ended			24 Months Ended
	Feb. 01, 2020	Feb. 02, 2019	Feb. 03, 2018	Feb. 01, 2020
Restructuring Cost and Reserve [Line Items]
Inventory charges	$ 9.2	$ 62.2	$ 0.0
Restructuring charges	69.9	63.7	$ 0.0
Non-cash charges	16.7	22.7
Signet Path to Brillance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	79.1	125.9		$ 205.0
Signet Path to Brillance \| Cost of sales
Restructuring Cost and Reserve [Line Items]
Inventory charges	9.2	62.2
Signet Path to Brillance \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Other Plan related expenses	69.9	63.7
Inventory charges \| Signet Path to Brillance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	9.2	62.2		71.4
Termination benefits \| Signet Path to Brillance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	16.1	9.7		25.8
Store closure and other costs \| Signet Path to Brillance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 53.8	$ 54.0		$ 107.8