- 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, 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
Income Tax Disclosure [Abstract]
Income tax provision at U.S. Federal statutory rate									$ 29.0	$ 98.0	$ 108.5
State income tax benefit, net of the U.S. Federal benefit									(4.0)	(2.9)	(1.7)
Foreign income taxed at rates different from the U.S. statutory rate									(40.0)	(57.1)	(54.5)
U.S. valuation allowance									2.9	2.1	1.7
Tax effect of non-deductible stock-based compensation									15.7	10.8	21.1
Research and development tax credit benefit									(7.2)	(8.8)	(7.0)
Tax (benefit) expense from closure of income tax audits and changes in uncertain tax positions									(0.7)	3.6	(2.8)
Tax effect of officer compensation in excess of $1.0 million									2.4	3.0	1.8
U.S. Manufacturer's deduction									0	(0.1)	(4.9)
Other									3.1	2.5	0.4
Income tax expense	$ (18.6)	$ 0.9	$ 11.6	$ 7.3	$ 2.4	$ 11.6	$ 20.1	$ 17.0	$ 1.2	$ 51.1	$ 62.6