Segment Information Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segments:
Revenue	$ 1,753.9	$ 1,742.0
Segment operating income (loss):	29.7	23.0
Interest expense	(20.9)	(22.6)
Interest income	5.2	5.8
Other income (expense), net	0.8	(19.2)
Income (loss) before income taxes	14.8	(13.0)
Depreciation and amortization of fixed assets and intangible assets	41.0	38.0
Capital expenditures	24.8	27.0
IAN
Segments:
Revenue	1,407.6	1,401.6
Segment operating income (loss):	43.8	41.8
Depreciation and amortization of fixed assets and intangible assets	29.5	27.6
Capital expenditures	17.2	20.3
CMG
Segments:
Revenue	346.3	340.4
Segment operating income (loss):	23.4	20.4
Depreciation and amortization of fixed assets and intangible assets	5.3	4.8
Capital expenditures	2.7	1.5
Corporate and Other
Segments:
Segment operating income (loss):	(37.5)	(39.2)
Depreciation and amortization of fixed assets and intangible assets	6.2	5.6
Capital expenditures	$ 4.9	$ 5.2