Segments - Revenue by Product (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			1
Total net revenues	$ 1,179.8	$ 1,257.8	$ 3,466.5	$ 3,787.7
Product
Segment Reporting Information [Line Items]
Total net revenues	794.7	869.7	2,330.4	2,615.8
Routing
Segment Reporting Information [Line Items]
Total net revenues	496.4	585.8	1,395.1	1,679.9
Switching
Segment Reporting Information [Line Items]
Total net revenues	221.1	212.6	705.9	730.2
Security
Segment Reporting Information [Line Items]
Total net revenues	77.2	71.3	229.4	205.7
Service
Segment Reporting Information [Line Items]
Total net revenues	$ 385.1	$ 388.1	$ 1,136.1	$ 1,171.9