Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue	$ 4,141.2	$ 3,623.8	$ 3,719.8	$ 3,468.9	$ 4,086.7	$ 3,714.3	$ 3,859.6	$ 3,629.6	$ 14,953.7	$ 15,290.2	$ 15,273.6
Americas
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue									8,882.2	8,900.0	9,180.8
Long-lived assets and goodwill	7,782.0				6,946.1				7,782.0	6,946.1	6,633.8
EMEA
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue									4,422.0	4,679.8	4,442.5
Long-lived assets and goodwill	3,061.3				2,578.9				3,061.3	2,578.9	2,840.8
Asia-Pacific
Revenue and Long-Lived Assets and Goodwill by Geographic Region
Revenue									1,649.5	1,710.4	1,650.3
Long-lived assets and goodwill	$ 658.9				$ 553.7				$ 658.9	$ 553.7	$ 553.8