Segment Information Major Geographic Area (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues and Long-Lived Assets
Revenue	$ 2,341.0	$ 1,902.6	$ 1,884.9	$ 1,753.9	$ 2,264.5	$ 1,922.2	$ 1,917.9	$ 1,742.0	$ 7,882.4	$ 7,846.6	$ 7,613.8
Long-Lived Assets	1,045.1				1,004.4				1,045.1	1,004.4
Domestic
Revenues and Long-Lived Assets
Revenue									4,714.3	4,684.8	4,475.5
Long-Lived Assets	705.5				684.8				705.5	684.8
Total International
Revenues and Long-Lived Assets
Revenue									3,168.1	3,161.8	3,138.3
Long-Lived Assets	339.6				319.6				339.6	319.6
United Kingdom
Revenues and Long-Lived Assets
Revenue									681.8	695.7	687.7
Long-Lived Assets	56.2				52.0				56.2	52.0
Continental Europe
Revenues and Long-Lived Assets
Revenue									716.1	699.8	697.2
Long-Lived Assets	73.6				57.0				73.6	57.0
Asia Pacific
Revenues and Long-Lived Assets
Revenue									913.6	923.0	916.9
Long-Lived Assets	115.5				118.3				115.5	118.3
Latin America
Revenues and Long-Lived Assets
Revenue									355.9	372.7	383.5
Long-Lived Assets	48.2				49.0				48.2	49.0
Other
Revenues and Long-Lived Assets
Revenue									500.7	470.6	$ 453.0
Long-Lived Assets	$ 46.1				$ 43.3				$ 46.1	$ 43.3