Investments - Summary of Available-for-sale Securities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Aug. 01, 2015	Aug. 02, 2014	Aug. 01, 2015	Aug. 02, 2014	Jan. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Marketable Securities, Realized Gain (Loss)	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Cost	23.5	22.5	23.5	22.5	$ 25.2
Unrealized Gain (Loss)	(0.3)	(0.2)	(0.3)	(0.2)	0.0
Fair Value	23.2	22.3	23.2	22.3	25.2
US Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Cost	9.2	10.0	9.2	10.0	9.7
Unrealized Gain (Loss)	(0.3)	(0.1)	(0.3)	(0.1)	(0.1)
Fair Value	8.9	9.9	8.9	9.9	9.6
US government agency securities
Schedule of Available-for-sale Securities [Line Items]
Cost	1.0	1.3	1.0	1.3	1.4
Unrealized Gain (Loss)	(0.1)	0.0	(0.1)	0.0	0.0
Fair Value	0.9	1.3	0.9	1.3	1.4
Corporate bonds and notes
Schedule of Available-for-sale Securities [Line Items]
Cost	9.9	8.7	9.9	8.7	10.6
Unrealized Gain (Loss)	0.0	(0.1)	0.0	(0.1)	0.2
Fair Value	9.9	8.6	9.9	8.6	10.8
Corporate equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost	3.4	2.5	3.4	2.5	3.5
Unrealized Gain (Loss)	0.1	0.0	0.1	0.0	(0.1)
Fair Value	$ 3.5	$ 2.5	$ 3.5	$ 2.5	$ 3.4