Common shares, treasury shares, reserves and dividends - Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended												12 Months Ended
	Jan. 30, 2021	Oct. 31, 2020	Aug. 01, 2020	May 02, 2020	Feb. 01, 2020	Nov. 02, 2019	Aug. 03, 2019	May 04, 2019	Feb. 02, 2019	Nov. 03, 2018	Aug. 04, 2018	May 05, 2018	Jan. 30, 2021	Feb. 01, 2020	Feb. 02, 2019
Class of Stock [Line Items]
Cash dividend per share (usd per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.37	$ 0.37	$ 0.37	$ 0.37	$ 0.37	$ 0.37	$ 0.37	$ 0.37	$ 0	$ 1.48	$ 1.48
Total dividends	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 19.4	$ 19.4	$ 19.3	$ 19.3	$ 19.2	$ 19.2	$ 19.2	$ 21.8	$ 0.0	$ 77.4	$ 79.4
Dividends payable					19.4									19.4
Dividends, preferred stock, cash													33.5	32.9	32.9
Series A Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Dividends, preferred stock, paid-in-kind	8.1	$ 8.0	$ 7.9	$ 7.8									31.8
Dividends, preferred stock, cash					$ 7.8	$ 7.8	$ 7.8	$ 7.8	7.8	$ 7.8	$ 7.8	$ 7.8		$ 31.2	31.2
Accrued Expenses
Class of Stock [Line Items]
Dividends payable	$ 8.1								$ 7.8				$ 8.1		$ 7.8