Investments - Summary of Available-for-sale Securities (Details) - USD ($) $ in Millions	Feb. 03, 2018	Jan. 28, 2017
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 28.1	$ 27.9
Unrealized Gain (Loss)	(0.2)	(0.7)
Fair Value	27.9	27.2
US Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Cost	8.3	8.8
Unrealized Gain (Loss)	(0.8)	(0.7)
Fair Value	7.5	8.1
US government agency securities
Schedule of Available-for-sale Securities [Line Items]
Cost	5.3	4.6
Unrealized Gain (Loss)	(0.2)	(0.2)
Fair Value	5.1	4.4
Corporate bonds and notes
Schedule of Available-for-sale Securities [Line Items]
Cost	11.0	11.0
Unrealized Gain (Loss)	(0.2)	(0.1)
Fair Value	10.8	10.9
Corporate equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost	3.5	3.5
Unrealized Gain (Loss)	1.0	0.3
Fair Value	$ 4.5	$ 3.8