Income Taxes Differences between the U.S. statutory rate and the aggregate income tax provision (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2011	Oct. 31, 2010	Jul. 31, 2010	Apr. 30, 2010	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Income tax provision at U. S. Federal statutory rate									$ 127.0	$ 95.2	$ 29.7
State income tax expense (benefit), net of the U.S. Federal benefit									2.8	1.4	(0.6)
Foreign income taxed at rates different from the U.S. statutory rate									(61.5)	(39.7)	(22.7)
U.S. valuation allowance									1.7	2.8	14.9
Non-deductible stock-based compensation									12.8	7.9	11.7
Research and development tax credit benefit									(6.0)	(5.6)	(4.7)
Tax benefit from closure of income tax audits and decreases in uncertain tax positions									(0.4)	(2.8)	(2.5)
Officer compensation in excess of $1.0 million									1.9	0.5	0.3
Goodwill impairment									0	0	0
Non-deductible in-process research and development charge									0	0	0
Other									(0.7)	0.3	0.6
Income Tax Expense (Benefit)	20.9	18.5	23.0	15.2	11.4	18.1	20.0	10.5	77.6	60.0	26.7
Expected Future Tax Rate
Other									$ 4.4	$ 2.1	$ 17.7