Segments, Geographical (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Revenues by Geographic Region [Line Items]
Net revenues	$ 1,239.5	$ 1,257.8	$ 1,308.9	$ 1,221.0	$ 1,385.6	$ 1,285.3	$ 1,221.3	$ 1,097.9	$ 5,027.2	$ 4,990.1	$ 4,857.8
Property and equipment, net and purchased intangible assets, net	1,149.2				1,194.0				1,149.2	1,194.0
Total Americas
Net Revenues by Geographic Region [Line Items]
Net revenues									2,947.2	2,968.8	2,792.2
United States
Net Revenues by Geographic Region [Line Items]
Net revenues									2,712.6	2,737.0	2,568.6
Property and equipment, net and purchased intangible assets, net	1,005.1				1,046.6				1,005.1	1,046.6
Other
Net Revenues by Geographic Region [Line Items]
Net revenues									234.6	231.8	223.6
Europe, Middle East, and Africa
Net Revenues by Geographic Region [Line Items]
Net revenues									1,195.8	1,238.1	1,320.3
Asia Pacific
Net Revenues by Geographic Region [Line Items]
Net revenues									884.2	783.2	$ 745.3
Total
Net Revenues by Geographic Region [Line Items]
Property and equipment, net and purchased intangible assets, net	$ 144.1				$ 147.4				$ 144.1	$ 147.4