Goodwill (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill
Goodwill		$ 3,674.4	$ 3,608.5	$ 3,669.2	[1]
Current year acquisitions		122.0	51.0
Foreign currency and other		(56.1)	(111.7)
IAN
Goodwill
Goodwill	[1]	3,043.8	3,051.4	3,108.5
Current year acquisitions		32.7	37.8
Foreign currency and other		(40.3)	(94.9)
CMG
Goodwill
Goodwill	[1]	630.6	557.1	$ 560.7
Current year acquisitions		89.3	13.2
Foreign currency and other		$ (15.8)	$ (16.8)

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