Segments - Revenue by Product (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			1
Total net revenues	$ 1,133.1	$ 1,179.8	$ 3,237.3	$ 3,466.5
Product
Segment Reporting Information [Line Items]
Total net revenues	743.2	794.7	2,075.8	2,330.4
Routing
Segment Reporting Information [Line Items]
Total net revenues	407.5	496.4	1,199.1	1,395.1
Switching
Segment Reporting Information [Line Items]
Total net revenues	241.6	221.1	633.6	705.9
Security
Segment Reporting Information [Line Items]
Total net revenues	94.1	77.2	243.1	229.4
Service
Segment Reporting Information [Line Items]
Total net revenues	$ 389.9	$ 385.1	$ 1,161.5	$ 1,136.1