Segments - Revenue by Product (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			1
Total net revenues	$ 1,138.2	$ 1,133.1	$ 3,222.5	$ 3,237.3
Product
Segment Reporting Information [Line Items]
Total net revenues	733.7	743.2	2,034.8	2,075.8
Routing
Segment Reporting Information [Line Items]
Total net revenues	432.0	407.5	1,149.7	1,199.1
Switching
Segment Reporting Information [Line Items]
Total net revenues	229.0	241.6	657.6	633.6
Security
Segment Reporting Information [Line Items]
Total net revenues	72.7	94.1	227.5	243.1
Service
Segment Reporting Information [Line Items]
Total net revenues	$ 404.5	$ 389.9	$ 1,187.7	$ 1,161.5