Investments - Summary of Available-for-sale Securities (Details) - USD ($) $ in Millions	Jan. 30, 2016	Jan. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 27.5	$ 25.2
Unrealized Gain (Loss)	(0.7)	0.0
Fair Value	26.8	25.2
US Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Cost	9.2	9.7
Unrealized Gain (Loss)	(0.4)	(0.1)
Fair Value	8.8	9.6
US government agency securities
Schedule of Available-for-sale Securities [Line Items]
Cost	4.0	1.4
Unrealized Gain (Loss)	0.0	0.0
Fair Value	4.0	1.4
Corporate bonds and notes
Schedule of Available-for-sale Securities [Line Items]
Cost	10.8	10.6
Unrealized Gain (Loss)	0.0	0.2
Fair Value	10.8	10.8
Corporate equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost	3.5	3.5
Unrealized Gain (Loss)	(0.3)	(0.1)
Fair Value	$ 3.2	$ 3.4