Goodwill (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Goodwill
Goodwill	$ 3,629.0		$ 3,580.6		$ 3,444.3	[1]
Current year acquisitions	75.3	[1]	133.7	[1]
Contingent and deferred payments for prior acquisitions	0	[1]	2.2	[1]	133.0
Other	(26.9)	[1],[2]	0.4	[1],[2]
IAN
Goodwill
Goodwill	3,109.3	[1]	3,074.6	[1]	2,952.9	[1]
Current year acquisitions	58.8	[1]	122.0	[1]
Contingent and deferred payments for prior acquisitions	0	[1]	2.2	[1]
Other	(24.1)	[1],[2]	(2.5)	[1],[2]
CMG
Goodwill
Goodwill	519.7	[1]	506.0	[1]	491.4	[1]
Current year acquisitions	16.5	[1]	11.7	[1]
Contingent and deferred payments for prior acquisitions	0	[1]	0	[1]
Other	$ (2.8)	[1],[2]	$ 2.9	[1],[2]

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

[2] Primarily includes foreign currency translation adjustments.