Segment Information Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financial Data:
Revenue	$ 1,876.1	$ 1,851.4	$ 3,552.1	$ 3,488.9
Operating Income (Loss)	215.8	195.8	223.6	184.1
Interest expense	20.3	22.6	41.2	42.8
Interest income	5.0	6.6	12.2	12.8
Other Nonoperating Income (Expense)	0.5	(11.2)	0.8	(9.5)
Income before income taxes	201.0	168.6	195.4	144.6
Depreciation and amortization of fixed assets and intangible assets	39.5	40.2	78.2	80.7
Capital expenditures	29.6	32.1	49.8	58.7
IAN
Financial Data:
Revenue	1,526.7	1,496.0	2,876.6	2,811.7
Operating Income (Loss)	205.0	184.0	236.6	195.5
Depreciation and amortization of fixed assets and intangible assets	30.2	30.2	59.6	61.7
Capital expenditures	20.4	17.2	32.5	31.1
CMG
Financial Data:
Revenue	349.4	355.4	675.5	677.2
Operating Income (Loss)	41.3	41.3	61.0	58.8
Depreciation and amortization of fixed assets and intangible assets	4.4	4.6	9.0	8.8
Capital expenditures	2.3	3.1	3.4	5.6
Corporate and Other
Financial Data:
Operating Income (Loss)	(30.5)	(29.5)	(74.0)	(70.2)
Depreciation and amortization of fixed assets and intangible assets	4.9	5.4	9.6	10.2
Capital expenditures	$ 6.9	$ 11.8	$ 13.9	$ 22.0