Retirement plans - Fair Value of Unfunded, Non-qualified Deferred Compensation Plans Assets (Details) - USD ($) $ in Millions	Feb. 01, 2020	Feb. 02, 2019
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 27.5	$ 33.9
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	21.0	26.9
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	6.5	7.0
Corporate-owned life insurance plans
Defined Benefit Plan Disclosure [Line Items]
Total assets	6.5	7.0
Corporate-owned life insurance plans | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	6.5	7.0
Money market funds
Defined Benefit Plan Disclosure [Line Items]
Total assets	21.0	26.9
Money market funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 21.0	$ 26.9