Segment Information Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Segments:
Line of Credit Facility, Covenant Compliance			June 30, 2014
Revenue	$ 1,851.4	$ 1,756.2	$ 3,488.9	$ 3,299.2
Operating Income (Loss)	195.8	174.8	184.1	132.4
Interest expense	22.6	37.5	42.8	74.3
Interest income	6.6	5.8	12.8	12.2
Other (expense) income, net	(11.2)	4.8	(9.5)	6.6
Income before income taxes	168.6	147.9	144.6	76.9
Depreciation and amortization of fixed assets and intangible assets	40.2	39.2	80.7	77.4
Capital expenditures	32.1	29.0	58.7	46.8
Assets	12,339.7		12,339.7		12,905.0
IAN
Segments:
Revenue	1,496.0	1,435.7	2,811.7	2,676.8
Operating Income (Loss)	184.0	169.2	195.5	146.6
Depreciation and amortization of fixed assets and intangible assets	30.2	31.6	61.7	62.5
Capital expenditures	17.2	13.5	31.1	23.5
Assets	11,175.2		11,175.2		11,425.1
CMG
Segments:
Revenue	355.4	320.5	677.2	622.4
Operating Income (Loss)	41.3	34.6	58.8	48.6
Depreciation and amortization of fixed assets and intangible assets	4.6	3.9	8.8	7.7
Capital expenditures	3.1	3.1	5.6	4.1
Assets	1,326.2		1,326.2		1,203.8
Corporate and Other
Segments:
Operating Income (Loss)	(29.5)	(29.0)	(70.2)	(62.8)
Depreciation and amortization of fixed assets and intangible assets	5.4	3.7	10.2	7.2
Capital expenditures	11.8	12.4	22.0	19.2
Assets	$ (161.7)		$ (161.7)		$ 276.1