Revenue recognition - ESP Deferred Revenue Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Aug. 01, 2020	Aug. 03, 2019	Aug. 01, 2020	Aug. 03, 2019
Change in Contract with Customer, Liability [Roll Forward]
ESP deferred revenue, beginning of period			$ 997.7
ESP deferred revenue, end of period	$ 1,030.2	$ 965.2	1,030.2	$ 965.2
Extended Service Plan
Change in Contract with Customer, Liability [Roll Forward]
ESP deferred revenue, beginning of period	961.0	931.3	960.0	927.6
Plans sold	55.7	90.5	109.4	186.5
Revenue recognized	(26.2)	(91.6)	(78.9)	(183.9)
ESP deferred revenue, end of period	990.5	$ 930.2	990.5	$ 930.2
Extended Service Plan and Voucher Promotions
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	$ (9.7)		$ (54.2)