Goodwill (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill
Goodwill		$ 3,608.5	$ 3,669.2	$ 3,629.0	[1]
Current year acquisitions		51.0	136.1
Foreign currency and other		(111.7)	(95.9)
IAN
Goodwill
Goodwill	[1]	3,051.4	3,108.5	3,097.0
Current year acquisitions		37.8	95.2
Foreign currency and other		(94.9)	(83.7)
CMG
Goodwill
Goodwill	[1]	557.1	560.7	$ 532.0
Current year acquisitions		13.2	40.9
Foreign currency and other		$ (16.8)	$ (12.2)

[1] For all periods presented, we have not recorded a goodwill impairment charge.