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, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Numerator:
Net income	$ 74.5	$ 29.4	$ 64.6	$ 78.9	$ 72.0	$ 72.8	$ 71.2	$ 69.3	$ 247.4	$ 285.3	$ 212.0
Denominator:
Denominator for basic net income per share-weighted average shares									226.4	227.7	227.6
Effect of dilutive securities									5.3	5.6	6.6
Denominator for dilutive net income per share									231.7	233.3	234.2
Basic net income per share	$ 0.33	$ 0.13	$ 0.28	$ 0.35	$ 0.32	$ 0.32	$ 0.31	$ 0.30	$ 1.09	$ 1.25	$ 0.93
Diluted net income per share	$ 0.32	$ 0.13	$ 0.28	$ 0.34	$ 0.31	$ 0.32	$ 0.30	$ 0.29	$ 1.07	$ 1.22	$ 0.90