Other Financial Information, Other Long-Term Assets (Details) - USD ($) $ in Millions	12 Months Ended		18 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Apr. 01, 2017	Oct. 01, 2014
Other Financial Information [Abstract]
Investments in privately-held companies	$ 62.7	$ 102.4
Promissory note in connection with the sale of Junos Pulse	57.9	132.9
Federal income tax receivable	43.8	28.9
Deferred tax asset	19.5	55.9
Inventory	4.1	8.4
Prepaid costs, deposits, and other	49.2	50.4
Other long-term assets	237.2	378.9
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Promissory note	132.9
Junos Pulse [Member]
Other Financial Information [Abstract]
Promissory note in connection with the sale of Junos Pulse				$ 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
Interest income	10.6	$ 6.3
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
Prepaid Expenses and Other Current Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Promissory note	$ 75.0