Summary of Significant Accounting Policies - Contract Revenue Adjustments on Income Statement (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net revenues:
Total net revenues	$ 1,179.8	$ 1,257.8	$ 3,466.5	$ 3,787.7
Operating expenses:
Sales and marketing	224.8	232.5	702.5	716.6
Without Adoption of Topic 606
Net revenues:
Total net revenues	1,184.4		3,486.0
Operating expenses:
Sales and marketing	225.4		697.6
Topic 606 Impact | Accounting Standards Update 2014-09
Net revenues:
Total net revenues	(4.6)		(19.5)
Operating expenses:
Sales and marketing	(0.6)		4.9
Product
Net revenues:
Total net revenues	794.7	869.7	2,330.4	2,615.8
Product | Without Adoption of Topic 606
Net revenues:
Total net revenues	771.9		2,249.7
Product | Topic 606 Impact | Accounting Standards Update 2014-09
Net revenues:
Total net revenues	22.8		80.7
Service
Net revenues:
Total net revenues	385.1	$ 388.1	1,136.1	$ 1,171.9
Service | Without Adoption of Topic 606
Net revenues:
Total net revenues	412.5		1,236.3
Service | Topic 606 Impact | Accounting Standards Update 2014-09
Net revenues:
Total net revenues	$ (27.4)		$ (100.2)