Net Income Per Share - Computation of Net Income Per Share Amounts (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Numerator:
Net income	$ 11.5	$ 10.7	$ 31.3	$ 28.3	$ 53.9	$ 57.6	$ 61.7	$ 55.6	$ 81.8	$ 228.8	$ 247.4
Denominator:
Denominator for basic net income per share—weighted average shares									227.1	224.0	226.4
Effect of dilutive securities									5.3	5.6	5.3
Denominator for dilutive net income per share									232.4	229.6	231.7
Basic net income per share (usd per share)	$ 0.05	$ 0.05	$ 0.14	$ 0.12	$ 0.24	$ 0.26	$ 0.28	$ 0.25	$ 0.36	$ 1.02	$ 1.09
Diluted net income per share (usd per share)	$ 0.05	$ 0.05	$ 0.13	$ 0.12	$ 0.23	$ 0.25	$ 0.27	$ 0.24	$ 0.35	$ 1.00	$ 1.07