Selected Quarterly Financial Information (Details) (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
Quarterly Financial Information Disclosure [Abstract]
Revenue, Net	$ 606.9	$ 548.0	$ 568.7	$ 588.6	$ 592.4	$ 548.6	$ 546.3	$ 528.3	$ 2,312.2	$ 2,215.6	$ 1,951.8
Gross Profit	544.9	490.1	508.9	529.8	534.9	489.0	488.9	473.7	2,073.7	1,986.5	1,755.2
Income from operations	84.6	34.4	92.9	94.0	91.8	90.2	95.0	78.6	305.9	355.6	271.4
Provision for income taxes	(11.6)	(4.9)	(27.5)	(18.6)	(20.9)	(18.5)	(23.0)	(15.2)	(62.6)	(77.6)	(60.0)
Net income	74.5	29.4	64.6	78.9	72.0	72.8	71.2	69.3	247.4	285.3	212.0
Earnings Per Share, Basic	$ 0.33	$ 0.13	$ 0.28	$ 0.35	$ 0.32	$ 0.32	$ 0.31	$ 0.30	$ 1.09	$ 1.25	$ 0.93
Earnings Per Share, Diluted	$ 0.32	$ 0.13	$ 0.28	$ 0.34	$ 0.31	$ 0.32	$ 0.30	$ 0.29	$ 1.07	$ 1.22	$ 0.90
income from operations includes following items [Abstract]
Stock-based compensation expense	37.5	51.9	33.5	33.4	30.0	25.6	27.3	25.9	156.3	108.8	80.7
Amortization of Acquired Intangible Assets	23.0	23.7	17.5	17.6	18.6	19.3	17.8	14.6	81.8	70.3
Restructuring Charges	$ 7.2	$ 36.7	$ 0	$ 0	$ 0	$ 0	$ (1.3)	$ 0	$ 43.9	$ (1.3)	$ 10.8