Investments - Summary of Available-for-sale Securities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2015	Nov. 01, 2014	Oct. 31, 2015	Nov. 01, 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	25.4	23.7	25.4	23.7	$ 25.2
Unrealized Gain (Loss)	(0.4)	(0.2)	(0.4)	(0.2)	0.0
Fair Value	25.0	23.5	25.0	23.5	25.2
US Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Cost	9.2	9.7	9.2	9.7	9.7
Unrealized Gain (Loss)	(0.4)	(0.1)	(0.4)	(0.1)	(0.1)
Fair Value	8.8	9.6	8.8	9.6	9.6
US government agency securities
Schedule of Available-for-sale Securities [Line Items]
Cost	2.3	1.4	2.3	1.4	1.4
Unrealized Gain (Loss)	0.0	(0.1)	0.0	(0.1)	0.0
Fair Value	2.3	1.3	2.3	1.3	1.4
Corporate bonds and notes
Schedule of Available-for-sale Securities [Line Items]
Cost	10.5	9.3	10.5	9.3	10.6
Unrealized Gain (Loss)	0.0	0.0	0.0	0.0	0.2
Fair Value	10.5	9.3	10.5	9.3	10.8
Corporate equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost	3.4	3.3	3.4	3.3	3.5
Unrealized Gain (Loss)	0.0	0.0	0.0	0.0	(0.1)
Fair Value	$ 3.4	$ 3.3	$ 3.4	$ 3.3	$ 3.4