Investments - Summary of Available-for-sale Securities (Details) - USD ($) $ in Millions	Jan. 28, 2017	Jan. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 27.9	$ 27.5
Unrealized Gain (Loss)	(0.7)	(0.7)
Fair Value	27.2	26.8
US Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Cost	8.8	9.2
Unrealized Gain (Loss)	(0.7)	(0.4)
Fair Value	8.1	8.8
US government agency securities
Schedule of Available-for-sale Securities [Line Items]
Cost	4.6	4.0
Unrealized Gain (Loss)	(0.2)	0.0
Fair Value	4.4	4.0
Corporate bonds and notes
Schedule of Available-for-sale Securities [Line Items]
Cost	11.0	10.8
Unrealized Gain (Loss)	(0.1)	0.0
Fair Value	10.9	10.8
Corporate equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost	3.5	3.5
Unrealized Gain (Loss)	0.3	(0.3)
Fair Value	$ 3.8	$ 3.2