Restructuring plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		42 Months Ended
	Jul. 31, 2021	Aug. 01, 2020	May 05, 2018	Jul. 31, 2021	Aug. 01, 2020	Jul. 31, 2021	Jan. 30, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0.9	$ (28.9)		$ 1.6	$ (41.6)
Signet Path to Brilliance
Restructuring Cost and Reserve [Line Items]
Restructuring plan, length			3 years
Restructuring charges	0.9	$ (28.7)		1.6	$ (41.0)	$ (251.0)
Restructuring reserve	7.2			7.2		7.2	$ 10.2
Signet Path to Brilliance | Accrued expenses and other current liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	5.0			5.0		5.0
Signet Path to Brilliance | Other noncurrent liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	$ 2.2			$ 2.2		$ 2.2