Other Financial Information, Other Income (Expense), Net (Details) - USD ($) $ in Millions		12 Months Ended
	Oct. 01, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Financial Information [Abstract]
Interest income		$ 35.4	$ 21.8	$ 10.0
Interest expense		(97.7)	(83.3)	(66.9)
Gain on legal settlement, net		0.0	0.0	196.1
(Loss) gain on investments, net		(1.8)	6.8	167.9
Gain on sale of Junos Pulse		0.0	0.0	19.6
Other		1.8	(5.1)	6.7
Other (expense) income, net		(62.3)	(59.8)	333.4
Interest expense, long-term debt		93.0	79.8	57.5
Capitalized interest		0.4	2.2	2.7
Cost-method investments, realized gains (loss)		(1.8)	6.8
Publicly-traded equity and privately-held investments, net realized gain				163.0
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on legal settlement, net		0.0	0.0	196.1
Promissory note in connection with the sale of Junos Pulse		57.9	132.9
Gain on sale of Junos Pulse		$ 0.0	$ 0.0	19.6
Junos Pulse [Member]
Other Financial Information [Abstract]
Gain on sale of Junos Pulse	$ 19.6
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration	230.7
Cash consideration	105.7
Working capital adjustment	19.3
Promissory note in connection with the sale of Junos Pulse	125.0
Gain on sale of Junos Pulse	$ 19.6
Palo Alto Networks [Member]
Other Financial Information [Abstract]
Gain on legal settlement, net				196.1
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on legal settlement, net				$ 196.1