Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	$ 3,719.5	$ 3,791.1	$ 11,097.1	$ 11,175.1
Americas
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	2,225.2	2,366.4	6,768.0	6,993.5
Long-lived assets and goodwill	6,657.0	6,577.0	6,657.0	6,577.0
United States
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	1,992.4	2,110.7	6,065.1	6,308.7
EMEA
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	1,083.1	1,005.8	3,137.6	3,008.1
Long-lived assets and goodwill	2,801.3	2,606.7	2,801.3	2,606.7
Asia Pacific
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	411.2	418.9	1,191.5	1,173.5
Long-lived assets and goodwill	$ 555.2	$ 541.3	$ 555.2	$ 541.3