Segment Information Operations (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segments:
Revenue	$ 1,726.5	$ 1,553.4	$ 4,942.0	$ 4,502.1
Segment operating income	173.0	101.6	302.7	220.3
Restructuring and other reorganization-related reversals (charges), net	0.2	(1.4)	(0.8)	(2.3)
Interest expense	(32.9)	(34.7)	(97.9)	(102.3)
Interest income	9.7	6.8	27.7	19.4
Other income (expense), net	137.1	(3.1)	136.3	(4.7)
Income before income taxes	287.1	69.2	368.0	130.4
Depreciation and amortization of fixed assets and intangible assets	36.2	37.3	109.5	111.5
Capital expenditures	30.2	21.4	83.3	49.7
IAN
Segments:
Segment revenue	1,432.7	1,284.7	4,140.3	3,757.1
Segment operating income	180.6	111.5	343.9	268.2
Depreciation and amortization of fixed assets and intangible assets	29.9	29.4	90.6	86.8
Capital expenditures	19.3	18.0	56.1	42.3
CMG
Segments:
Segment revenue	293.8	268.7	801.7	745.0
Segment operating income	27.9	23.8	66.6	53.3
Depreciation and amortization of fixed assets and intangible assets	3.1	3.7	9.5	10.7
Capital expenditures	3.3	1.8	7.5	3.7
Corporate and Other
Segments:
Segment operating income	(35.5)	(33.7)	(107.8)	(101.2)
Depreciation and amortization of fixed assets and intangible assets	3.2	4.2	9.4	14.0
Capital expenditures	$ 7.6	$ 1.6	$ 19.7	$ 3.7