Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	$ 3,859.6	$ 3,790.1	$ 7,489.2	$ 7,377.6
Americas
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	2,212.5	2,296.8	4,306.6	4,542.7
Long-lived assets and goodwill	6,825.4	6,654.2	6,825.4	6,654.2
United States
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	1,990.8	2,060.9	3,871.9	4,072.7
EMEA
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	1,212.8	1,088.0	2,356.3	2,054.6
Long-lived assets and goodwill	2,757.9	2,678.0	2,757.9	2,678.0
Asia Pacific
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	434.3	405.3	826.3	780.3
Long-lived assets and goodwill	$ 556.5	$ 537.5	$ 556.5	$ 537.5