Investments - Summary of Available-for-sale Securities (Details) - USD ($) $ in Millions	Feb. 02, 2019	Feb. 03, 2018
Debt Securities, Available-for-sale [Line Items]
Cost	$ 15.7	$ 28.1
Unrealized Gain (Loss)	(0.9)	(0.2)
Fair Value	14.8	27.9
US Treasury securities
Debt Securities, Available-for-sale [Line Items]
Cost	5.1	8.3
Unrealized Gain (Loss)	(0.4)	(0.8)
Fair Value	4.7	7.5
US government agency securities
Debt Securities, Available-for-sale [Line Items]
Cost	2.6	5.3
Unrealized Gain (Loss)	(0.1)	(0.2)
Fair Value	2.5	5.1
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Cost	5.3	11.0
Unrealized Gain (Loss)	(0.1)	(0.2)
Fair Value	5.2	10.8
Corporate equity securities
Debt Securities, Available-for-sale [Line Items]
Cost	2.7	3.5
Unrealized Gain (Loss)	(0.3)	1.0
Fair Value	$ 2.4	$ 4.5