Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	$ 3,714.3	$ 3,719.5	$ 11,203.5	$ 11,097.1
Americas
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	2,197.5	2,225.2	6,504.2	6,768.0
Long-lived assets and goodwill	6,930.2	6,657.0	6,930.2	6,657.0
United States
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	1,992.7	1,992.4	5,864.6	6,065.1
EMEA
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	1,078.9	1,083.1	3,435.1	3,137.6
Long-lived assets and goodwill	2,611.1	2,801.3	2,611.1	2,801.3
Asia Pacific
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	437.9	411.2	1,264.2	1,191.5
Long-lived assets and goodwill	$ 552.1	$ 555.2	$ 552.1	$ 555.2