Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue	$ 4,241.8	$ 3,791.1	$ 3,884.9	$ 3,499.1	$ 4,153.3	$ 3,706.6	$ 3,805.3	$ 3,469.2	$ 15,416.9	$ 15,134.4	$ 15,317.8
Americas
Revenue									9,597.6	9,359.0	9,111.7
Long-lived assets and goodwill	6,662.7				6,103.4				6,662.7	6,103.4	6,157.8
United States
Revenue									8,627.8	8,526.7	8,185.9
EMEA
Revenue									4,183.1	4,203.5	4,602.5
Long-lived assets and goodwill	2,469.1				2,737.8				2,469.1	2,737.8	2,800.8
Asia Pacific
Revenue									1,636.2	1,571.9	1,603.6
Long-lived assets and goodwill	$ 519.1				$ 527.9				$ 519.1	$ 527.9	$ 571.6