Segment Reporting (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue	$ 4,195.1	$ 3,749.6	$ 3,870.9	$ 3,502.2	$ 4,058.1	$ 3,490.5	$ 3,637.0	$ 3,398.9	$ 15,317.8	$ 14,584.5	$ 14,219.4
Americas
Revenue									9,121.3	8,597.1	8,375.8
Long-lived assets and goodwill	6,157.8				6,082.6				6,157.8	6,082.6	6,066.3
United States
Revenue									8,152.7	7,569.7	7,363.7
EMEA
Revenue									4,594.0	4,407.4	4,285.0
Long-lived assets and goodwill	2,800.8				2,984.6				2,800.8	2,984.6	2,875.2
Asia Pacific
Revenue									1,602.5	1,580.0	1,558.6
Long-lived assets and goodwill	$ 571.6				$ 586.2				$ 571.6	$ 586.2	$ 626.5