Segment Information Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financial Data:
Revenue	$ 1,865.5	$ 1,841.1	$ 5,417.6	$ 5,330.0
OPERATING INCOME	191.9	171.3	415.5	355.4
Interest expense	(21.3)	(20.7)	(62.5)	(63.5)
Interest income	5.6	7.5	17.8	20.3
Other expense, net	(37.2)	(0.6)	(36.4)	(10.1)
Income before income taxes	139.0	157.5	334.4	302.1
Depreciation and amortization of fixed assets and intangible assets	38.1	41.0	116.3	121.7
Capital expenditures	30.9	35.7	80.7	94.4
IAN
Financial Data:
Revenue	1,484.1	1,459.3	4,351.3	4,260.3
OPERATING INCOME	182.9	164.7	419.2	359.1
Depreciation and amortization of fixed assets and intangible assets	27.9	31.0	87.5	92.6
Capital expenditures	23.0	20.8	55.4	51.9
CMG
Financial Data:
Revenue	381.4	381.8	1,066.3	1,069.7
OPERATING INCOME	48.2	47.8	109.5	107.7
Depreciation and amortization of fixed assets and intangible assets	4.9	4.9	13.9	13.8
Capital expenditures	2.3	2.7	5.8	8.3
Corporate and Other
Financial Data:
OPERATING INCOME	(39.2)	(41.2)	(113.2)	(111.4)
Depreciation and amortization of fixed assets and intangible assets	5.3	5.1	14.9	15.3
Capital expenditures	$ 5.6	$ 12.2	$ 19.5	$ 34.2