Selected Quarterly Financial Information (Unaudited) (Details) (USD $) In Millions, except Per Share data, 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
Quarterly Financial Information Disclosure [Abstract]
Net revenue	$ 664.6	$ 618.0	$ 637.1	$ 592.5	$ 586.6	$ 555.2	$ 561.7	$ 570.4	$ 2,512.2	$ 2,273.9	$ 2,312.2
Gross profit	575.1	532.0	549.2	513.8	514.7	488.1	493.9	502.9	2,170.1	1,999.6	2,073.7
Income from operations	14.0	14.6	49.9	42.2	51.7	68.1	83.6	81.4	120.7	284.8	305.9
Provision for income taxes	18.6	(0.9)	(11.6)	(7.3)	(2.4)	(11.6)	(20.1)	(17.0)	(1.2)	(51.1)	(62.6)
Net income	11.5	10.7	31.3	28.3	53.9	57.6	61.7	55.6	81.8	228.8	247.4
Basic net income per share	$ 0.05	$ 0.05	$ 0.14	$ 0.12	$ 0.24	$ 0.26	$ 0.28	$ 0.25	$ 0.36	$ 1.02	$ 1.09
Diluted net income per share	$ 0.05	$ 0.05	$ 0.13	$ 0.12	$ 0.23	$ 0.25	$ 0.27	$ 0.24	$ 0.35	$ 1.00	$ 1.07
Income from operations includes following items [Abstract]
Stock-based compensation expense	49.1	43.1	39.8	33.6	36.1	31.6	31.0	33.5	165.6	132.2	156.3
Amortization of acquisition related intangibles	21.9	22.6	24.6	23.9	20.6	18.2	20.3	21.6	93.0	80.7
Additions	$ 0	$ 0	$ 0.8	$ 2.3	$ 6.3	$ 4.4	$ 1.7	$ 0.4	$ 3.1	$ 12.8	$ 43.9