Segment Information Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011		Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segments:
Revenue	$ 2,072.6	$ 1,726.5		$ 1,740.7	$ 1,474.8	$ 2,005.2	$ 1,553.4	$ 1,611.7	$ 1,337.0	$ 7,014.6	$ 6,507.3	$ 6,007.4
Segment operating income										688.2	552.6	345.9
Restructuring and other reorganization-related charges, net	(0.2)	0.2		(0.2)	(0.8)	(1.6)	(1.4)	(0.6)	(0.3)	(1.0)	(3.9)	(4.6)
Interest expense										(136.8)	(139.7)	(155.6)
Interest income										37.8	28.7	35.0
Other income, net	13.9	137.1	[1]	5.3	(6.1)	17.6	(3.1)	(2.1)	0.5	150.2	12.9	11.7
Income before income taxes										738.4	450.6	232.4
Depreciation and amortization of fixed assets and intangible assets										150.9	148.4	169.9
Capital expenditures										140.3	96.3	67.1
IAN
Segments:
Segment revenue										5,891.8	5,468.4	5,061.7
Segment operating income										728.8	617.6	423.4
Depreciation and amortization of fixed assets and intangible assets										125.7	116.7	131.6
Capital expenditures										94.1	83.5	50.0
CMG
Segments:
Segment revenue										1,122.8	1,038.9	945.7
Segment operating income										101.4	80.3	73.1
Depreciation and amortization of fixed assets and intangible assets										12.8	14.2	15.0
Capital expenditures										16.9	6.9	5.7
Corporate and other
Segments:
Segment operating income										(142.0)	(145.3)	(150.6)
Depreciation and amortization of fixed assets and intangible assets										12.4	17.5	23.3
Capital expenditures										$ 29.3	$ 5.9	$ 11.4

[1] The three months ended September 30, 2011, includes a pre-tax gain of $132.2 related to the sale of approximately half of our holdings in Facebook, Inc.