Other Financial Information, Other Long-Term Assets (Details) - USD ($) $ in Millions	12 Months Ended		18 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Apr. 01, 2017	Oct. 01, 2014
Other Financial Information [Abstract]
Privately-held investments	$ 102.4	$ 89.9
Licensed software	7.1	8.6
Federal income tax receivable	28.9	20.0
Customer financing receivable	0.0	16.9
Inventory	8.4	8.0
Prepaid costs, deposits, and other	110.5	75.1
Other long-term assets	390.2	343.5
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Interest income	6.3	1.6
Junos Pulse [Member]
Other Financial Information [Abstract]
Promissory note in connection with the sale of Junos Pulse	$ 132.9	$ 125.0		$ 125.0
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
Scenario, Forecast [Member] | Junos Pulse [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Minimum payment due on or prior to April 1, 2017			$ 75.0