Goodwill and Purchased Intangible Assets - GoodwillRollforward (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) Reportable_Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 3,108,800,000	$ 3,096,200,000
Additions due to business combination	228,300,000	14,400,000
Other		(1,800,000)
Goodwill, end of period	$ 3,337,100,000	3,108,800,000	$ 3,096,200,000
Number of reporting units | Reportable_Segment	3
Goodwill impairment	$ 0	$ 0	$ 0