Business Combinations - Estimated Fair Values of Aggregate Assets and Liabilities Acquired (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Fair Value Of Assets And Liabilities Statement [Line Items]
Recorded earn-out payable	$ 40.2	$ 16.9
Other Acquisitions
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash paid	127.2
Other payable	2.3
Recorded earn-out payable	40.2
Total consideration	169.7
Maximum potential earn-out payable	74.2
Allocation of purchase price:
Cash and equivalents	4.9
Fiduciary cash	7.0
Fiduciary receivables	9.0
Other current assets	11.1
Goodwill	116.8
Deferred income tax, net	19.1
Other assets	0.2
Total assets acquired	195.0
Fiduciary liabilities	(16.0)
Other current liabilities	(6.3)
Other long-term liabilities	(3.0)
Total liabilities assumed	(25.3)
Net assets acquired	169.7
Other Acquisitions | Purchased Customer Accounts and Other
Allocation of purchase price:
Intangible assets	26.6
Other Acquisitions | Non-compete Agreements
Allocation of purchase price:
Intangible assets	$ 0.3