Acquisitions Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Number of businesses acquired	0	4
Goodwill and intangible assets related to acquisitions		$ 28.0	$ 7.6
Interest income	$ 29.7	$ 29.5	$ 34.5
IAN
Number of businesses acquired		3	1
DXTRA
Number of businesses acquired		1

Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Interest income derived from funds deposited with both domestic and foreign financial institutions including funds in money market and other accounts.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 220
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1402
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