Acquisitions Acxiom Acquisition (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2022
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Gross	$ 1,360.3	$ 1,330.0
Cash and Cash Equivalents, at Carrying Value	2,545.3	3,270.0
Accounts receivable, net of allowance	5,316.0	5,177.7
Accounts receivable, billable to clients	2,023.0	2,347.2
Other current assets	435.0	428.7
Property, Plant and Equipment, Net	637.4	675.8
Goodwill	5,050.6	4,908.7	$ 4,945.5	$ 4,908.7
Other non-current assets	464.5	399.6
Contract liabilities	(680.0)	(688.5)
Other non-current liabilities	(572.6)	(600.7)
Net revenue	9,449.4	9,107.9	8,064.5
Net Income Attributable to Parent	938.0	952.8	351.1
Goodwill and intangible assets related to acquisitions			$ 28.0
Customer Lists [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Gross	873.1	855.7
know-how technology [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Gross	239.2	235.3
Trade Names [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Gross	$ 231.8	$ 222.8