Business Combinations - Additional Information (Details) $ in Millions		3 Months Ended
	Mar. 31, 2023 USD ($)	Mar. 31, 2023 USD ($) Acquisition	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Business Acquisition [Line Items]
Number of acquisitions | Acquisition		7
Purchase price of acquisitions		$ 2.9
Payments to Acquire Businesses, Gross	$ 3.6	44.7
Payments for businesses acquired, net of cash acquired		37.6	$ 436.0
Net assets acquired	64.5	64.5
Goodwill, Acquired During Period		23.0
Goodwill currently deductible for income tax purposes	1.1	1.1
Goodwill currently non-deductible for income tax purposes	21.7	21.7
Goodwill related to the recorded earn-out payables	0.2	0.2
Total revenues related to acquisitions		2.6
Income before income taxes related to acquisitions		1.0
Estimated acquisition earn-out payables	254.2	254.2	$ 250.9	$ 251.6	$ 291.0
Maximum Future Contingency payments Acquisitions	535.9	535.9
Other Noncurrent Liabilities
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	109.6	109.6
Accounts payable
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	144.6	144.6
Retail
Business Acquisition [Line Items]
Goodwill, Acquired During Period		44.6
National Programs
Business Acquisition [Line Items]
Goodwill, Acquired During Period		(21.6)
Wholesale Brokerage
Business Acquisition [Line Items]
Goodwill, Acquired During Period		$ 0.0
Purchased Customer Accounts
Business Acquisition [Line Items]
Weighted average life (years)		15 years
Non-compete Agreements
Business Acquisition [Line Items]
Weighted average life (years)		5 years
Assets and Assumed Certain Liabilities
Business Acquisition [Line Items]
Number of acquisitions | Acquisition		1
Other Acquisitions
Business Acquisition [Line Items]
Net assets acquired	64.5	$ 64.5
Other Acquisitions | Maximum
Business Acquisition [Line Items]
Net assets acquired	50.0	50.0
GRP Holdco Limited
Business Acquisition [Line Items]
Maximum potential earn-out amount	$ 0.0	$ 0.0