Goodwill (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Goodwill
Goodwill	$ 3,444.3	[1]	$ 3,368.5	[1]	$ 3,321.0	[1]
Current year acquisitions	96.9	[1]	38.8	[1]
Contingent and deferred payments for prior acquisitions	0.8	[1]	35.1	[1]
Other	(21.9)	[1],[2]	(26.4)	[1],[2]
IAN
Goodwill
Goodwill	2,952.9	[1]	2,906.0	[1]	2,844.7	[1]
Current year acquisitions	68.5	[1]	37.5	[1]
Contingent and deferred payments for prior acquisitions	0.8	[1]	34.4	[1]
Other	(22.4)	[1],[2]	(10.6)	[1],[2]
CMG
Goodwill
Goodwill	491.4	[1]	462.5	[1]	476.3	[1]
Current year acquisitions	28.4	[1]	1.3	[1]
Contingent and deferred payments for prior acquisitions	0	[1]	0.7	[1]
Other	$ 0.5	[1],[2]	$ (15.8)	[1],[2]

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

[2] Primarily includes foreign currency translation adjustments.