Segment Information Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segments:
Revenue	$ 1,715.7	$ 1,740.7	$ 3,222.5	$ 3,215.5
Segment operating income	176.4	174.0	137.0	128.7
Interest expense	(32.7)	(33.1)	(65.3)	(65.0)
Interest income	6.7	9.7	14.7	18.0
Other income (expense), net	4.7	5.3	3.4	(0.8)
Income before income taxes	155.1	155.9	89.8	80.9
Depreciation and amortization of fixed assets and intangible assets	36.8	37.7	71.4	73.3
Capital expenditures	35.8	36.2	58.2	53.1
IAN
Segments:
Segment revenue	1,423.3	1,471.7	2,667.2	2,707.6
Segment operating income	177.3	184.7	162.0	162.5
Depreciation and amortization of fixed assets and intangible assets	29.9	31.4	58.3	60.7
Capital expenditures	19.9	22.8	32.7	36.8
CMG
Segments:
Segment revenue	292.4	269.0	555.3	507.9
Segment operating income	31.2	27.8	38.7	38.5
Depreciation and amortization of fixed assets and intangible assets	3.3	3.3	6.7	6.4
Capital expenditures	3.6	2.9	5.6	4.2
Corporate and other
Segments:
Segment operating income	(32.1)	(38.5)	(63.7)	(72.3)
Depreciation and amortization of fixed assets and intangible assets	3.6	3.0	6.4	6.2
Capital expenditures	$ 12.3	$ 10.5	$ 19.9	$ 12.1