Goodwill (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Goodwill
Goodwill	$ 3,580.6		$ 3,444.3		$ 3,368.5	[1]
Current year acquisitions	133.7	[1]	96.9	[1]
Contingent and deferred payments for prior acquisitions	2.2	[1]	0.8	[1]
Other	0.4	[1],[2]	(21.9)	[1],[2]
IAN
Goodwill
Goodwill	3,074.6	[1]	2,952.9	[1]	2,906.0	[1]
Current year acquisitions	122.0	[1]	68.5	[1]
Contingent and deferred payments for prior acquisitions	2.2	[1]	0.8	[1]
Other	(2.5)	[1],[2]	(22.4)	[1],[2]
CMG
Goodwill
Goodwill	506.0	[1]	491.4	[1]	462.5	[1]
Current year acquisitions	11.7	[1]	28.4	[1]
Contingent and deferred payments for prior acquisitions	0	[1]	0	[1]
Other	$ 2.9	[1],[2]	$ 0.5	[1],[2]

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

[2] Primarily includes foreign currency translation adjustments.