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Restructuring plans - Restructuring and Related Costs (Details) - USD ($) $ in Millions	12 Months Ended			36 Months Ended
	Jan. 30, 2021	Feb. 01, 2020	Feb. 02, 2019	Jan. 30, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 46.2	$ 69.9	$ 63.7
Signet Path to Brillance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	47.6	79.1	125.9	$ 252.6
Non-cash charges				126.9
Signet Path to Brillance \| Cost of sales
Restructuring Cost and Reserve [Line Items]
Inventory charges	1.4	9.2	62.2
Signet Path to Brillance \| Restructuring charges
Restructuring Cost and Reserve [Line Items]
Other Plan related expenses	46.2	69.9	63.7
Non-cash charges	14.7	16.7	22.7
Inventory charges \| Signet Path to Brillance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.4	9.2	62.2	72.8
Termination benefits \| Signet Path to Brillance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	24.1	16.1	9.7	49.9
Store closure and other costs \| Signet Path to Brillance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 22.1	$ 53.8	$ 54.0	$ 129.9