Components of Other Comprehensive Income (Loss), Net of Taxes (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010
Net income	$ 72.8	$ 53.6	$ 213.3	$ 150.4
Other comprehensive income
Net gain (loss) on derivative instruments, net of taxes	(3.3)	(13.0)	(2.8)	(10.0)
Change in net unrealized gain on available-for-sale securities, net of tax	(1.4)	0.9	(0.4)	1.8
Net change in cumulative foreign currency translation gain (loss)	(6.2)	11.0	7.2	7.7
Total other comprehensive income (loss)	(10.9)	(1.1)	4.0	(0.5)
Total comprehensive income	$ 61.9	$ 52.5	$ 217.3	$ 149.9