Segment Information Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segments:
Revenue	$ 1,756.2	$ 1,715.7	$ 3,299.2	$ 3,222.5
Operating income (loss)	174.8	176.4	132.4	137.0
Interest expense	(37.5)	(32.7)	(74.3)	(65.3)
Interest income	5.8	6.7	12.2	14.7
Other income, net	4.8	4.7	6.6	3.4
Income before income taxes	147.9	155.1	76.9	89.8
Depreciation and amortization of fixed assets and intangible assets	39.2	36.8	77.4	71.4
Capital expenditures	29.0	35.8	46.8	58.2
IAN
Segments:
Segment revenue	1,435.7	1,423.3	2,676.8	2,667.2
Operating income (loss)	169.2	177.3	146.6	162.0
Depreciation and amortization of fixed assets and intangible assets	31.6	29.9	62.5	58.3
Capital expenditures	13.5	19.9	23.5	32.7
CMG
Segments:
Segment revenue	320.5	292.4	622.4	555.3
Operating income (loss)	34.6	31.2	48.6	38.7
Depreciation and amortization of fixed assets and intangible assets	3.9	3.3	7.7	6.7
Capital expenditures	3.1	3.6	4.1	5.6
Corporate and other
Segments:
Operating income (loss)	(29.0)	(32.1)	(62.8)	(63.7)
Depreciation and amortization of fixed assets and intangible assets	3.7	3.6	7.2	6.4
Capital expenditures	$ 12.4	$ 12.3	$ 19.2	$ 19.9