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, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012
Income Tax Disclosure [Abstract]
Income tax provision at U.S. Federal statutory rate									$ 98.0	$ 108.5	$ 127.0
State income tax (benefit) expense, net of the U.S. Federal benefit									(2.9)	(1.7)	2.8
Foreign income taxed at rates different from the U.S. statutory rate									(57.1)	(54.5)	(61.5)
U.S. valuation allowance									2.1	1.7	1.7
Non-deductible stock-based compensation									10.8	21.1	12.8
Research and development tax credit benefit									(8.8)	(7.0)	(6.0)
Tax expense (benefit) from closure of income tax audits and changes in uncertain tax positions									3.6	(2.8)	(0.4)
Officer compensation in excess of $1.0 million									3.0	1.8	1.9
U.S. Manufacturer's deduction									(0.1)	(4.9)	(3.0)
Other									2.5	0.4	2.3
Income tax expense	$ 2.4	$ 11.6	$ 20.1	$ 17.0	$ 11.6	$ 4.9	$ 27.5	$ 18.6	$ 51.1	$ 62.6	$ 77.6