Segment Operations (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) numberOfPeople	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segments:
Number of Reportable Segments | numberOfPeople	2
EBITA	$ 1,522.4	$ 674.3	$ 1,172.0
Total (expenses) and other income	(214.1)	(227.1)	(207.7)
Total revenue	10,240.7	9,061.0	10,221.3
Net revenue	9,107.9	8,064.5	8,625.1
Operating Income (Loss)	1,436.2	588.4	1,086.0
Amortization of Intangible Assets	86.2	85.9	86.0
Interest expense	(173.1)	(192.2)	(199.3)
Interest income	29.7	29.5	34.5
Other expense, net	(70.7)	(64.4)	(42.9)
Income before income taxes	1,222.1	361.3	878.3
Depreciation and amortization	197.6	204.7	192.5
Capital expenditures	195.3	167.5	198.5
Assets	19,909.2	18,042.7
IAN
Segments:
EBITA	1,465.3	699.1	1,115.7
Total revenue	8,419.4	7,410.1	7,992.0
Net revenue	7,839.8	6,921.4	7,328.8
Amortization of Intangible Assets	81.7	81.5	81.6
Depreciation and amortization	172.0	178.9	164.6
Capital expenditures	157.3	132.0	161.8
Assets	15,596.1	14,784.5
DXTRA
Segments:
EBITA	186.5	56.5	158.1
Total revenue	1,821.3	1,650.9	2,229.3
Net revenue	1,268.1	1,143.1	1,296.3
Amortization of Intangible Assets	4.5	4.4	4.4
Depreciation and amortization	16.4	20.4	20.6
Capital expenditures	8.1	8.4	13.3
Assets	1,579.5	1,549.2
Corporate and Other
Segments:
EBITA	(129.4)	(81.3)	(101.8)
Amortization of Intangible Assets	0.0	0.0	0.0
Depreciation and amortization	9.2	5.4	7.3
Capital expenditures	29.9	27.1	$ 23.4
Assets	$ 2,733.6	$ 1,709.0