Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segments:
Total revenue	$ 2,359.8	$ 2,361.2
Net revenue	1,972.1	2,004.8
Segment EBITA	97.2	71.8
Amortization of acquired intangibles	(21.3)	(21.6)
Depreciation	51.5	49.5
Capital expenditures	44.6	32.8
Total assets	16,428.9		$ 17,751.9
Operating income	75.9	50.2
Total (expenses) and other income	(55.9)	(48.9)
Income before income taxes	20.0	1.3
IAN
Segments:
Total revenue	1,818.8	1,862.2
Net revenue	1,664.5	1,706.1
Segment EBITA	99.0	116.0
Amortization of acquired intangibles	(20.2)	(20.5)
Depreciation	44.7	42.1
Capital expenditures	33.7	26.5
Total assets	13,640.9		15,155.2
CMG
Segments:
Total revenue	541.0	499.0
Net revenue	307.6	298.7
Segment EBITA	22.3	0.4
Amortization of acquired intangibles	(1.1)	(1.1)
Depreciation	5.1	4.8
Capital expenditures	1.6	1.0
Total assets	1,650.4		1,725.5
Corporate and Other
Segments:
Segment EBITA	(24.1)	(44.6)
Amortization of acquired intangibles	(0.0)	(0.0)
Depreciation	1.7	2.6
Capital expenditures	9.3	$ 5.3
Total assets	$ 1,137.6		$ 871.2