Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions							3 Months Ended								12 Months Ended
	Oct. 22, 2015	Jul. 23, 2015	Apr. 23, 2015	Jan. 27, 2015	Oct. 23, 2014	Jul. 22, 2014	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net revenues:
Product							$ 973.9	$ 925.4	$ 899.7	$ 764.1	$ 794.0	$ 809.5	$ 929.2	$ 876.0	$ 3,563.1	$ 3,408.7	$ 3,519.9
Service							345.7	323.2	322.5	303.3	307.6	316.4	300.3	294.1	1,294.7	1,218.4	1,149.2
Total net revenues							1,319.6	1,248.6	1,222.2	1,067.4	1,101.6	1,125.9	1,229.5	1,170.1	4,857.8	4,627.1	4,669.1
Cost of revenues:
Product							346.5	322.6	311.7	288.8	310.9	290.0	359.3	326.6	1,269.6	1,286.8	1,276.6
Service							130.7	128.6	129.0	121.3	115.6	121.1	122.0	123.4	509.6	482.1	451.1
Total cost of revenues							477.2	451.2	440.7	410.1	426.5	411.1	481.3	450.0	1,779.2	1,768.9	1,727.7
Gross margin							842.4	797.4	781.5	657.3	675.1	714.8	748.2	720.1	3,078.6	2,858.2	2,941.4
Operating expenses:
Research and development							247.2	247.0	251.6	248.7	233.5	253.2	255.5	264.0	994.5	1,006.2	1,043.2
Sales and marketing							255.9	235.3	232.4	220.2	243.0	249.2	258.0	273.4	943.8	1,023.6	1,075.9
General and administrative							60.3	57.1	56.3	55.2	40.6	55.0	60.6	74.9	228.9	231.1	217.3
Restructuring and other (benefits) charges							(0.1)	0.0	(1.9)	1.4	9.8	(15.0)	58.2	114.0	(0.6)	167.0	39.1
Impairment of goodwill											850.0	0.0	0.0	0.0	0.0	850.0	0.0
Total operating expenses							563.3	539.4	538.4	525.5	1,376.9	542.4	632.3	726.3	2,166.6	3,277.9	2,375.5
Operating income (loss)							279.1	258.0	243.1	131.8	(701.8)	172.4	115.9	(6.2)	912.0	(419.7)	565.9
Other (expense) income, net							(18.5)	(8.4)	(17.1)	(15.8)	7.4	(6.8)	178.6	154.2	(59.8)	333.4	(40.4)
Income (loss) before income taxes							260.6	249.6	226.0	116.0	(694.4)	165.6	294.5	148.0	852.2	(86.3)	525.5
Income tax provision							62.8	51.9	68.0	35.8	75.2	62.0	73.4	37.4	218.5	248.0	85.7
Net income (loss)							$ 197.8	$ 197.7	$ 158.0	$ 80.2	$ (769.6)	$ 103.6	$ 221.1	$ 110.6	$ 633.7	$ (334.3)	$ 439.8
Net income (loss) per share:
Basic (in dollars per share)							$ 0.52	$ 0.52	$ 0.41	$ 0.20	$ (1.81)	$ 0.23	$ 0.47	$ 0.23	$ 1.62	$ (0.73)	$ 0.88
Diluted (in dollars per share)							0.51	0.51	0.40	0.19	(1.81)	0.23	0.46	0.22	$ 1.59	$ (0.73)	$ 0.86
Shares used in computing net income per share:
Basic (in shares)															390.6	457.4	501.8
Diluted (in shares)															399.4	457.4	510.3
Cash dividends declared per share of common stock (in dollars per share)	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0	$ 0	$ 0.40	$ 0.20	$ 0