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Business Acquisitions Purchase Price Allocation Goodwill Amount

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Business acquisitionsnet earnings before interest, income taxes, depreciation, amortization and change in estimated acquisition earnout payables.

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Business combination, recognized identifiable assets acquired and liabilities assumed, intangible assets, non-compete agreements.

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Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Trade Names

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Fair Value Inputs, Attrition Rate

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Value of input used to measure alternative investment.

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Amount after tax of pro forma income from continuing operations as if the business combination had been completed at the beginning of a period.

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of deferred tax liability attributable to taxable temporary differences.

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Business Combinations - Additional Information (Detail) $ in Millions						3 Months Ended		9 Months Ended		285 Months Ended
	Aug. 18, 2025 USD ($) employee	Apr. 10, 2025 USD ($) office employee	Jan. 07, 2025 USD ($)	Dec. 19, 2024 USD ($)	Dec. 11, 2024 USD ($)	Sep. 30, 2025 USD ($) acquisition	Sep. 30, 2024 USD ($) acquisition	Sep. 30, 2025 USD ($) acquisition	Sep. 30, 2024 USD ($) acquisition	Sep. 30, 2025 USD ($) company
Business Acquisition [Line Items]
Cash raised through follow-on common stock offering								$ 1,481.3	$ 138.0
Accretion of the discount on acquisition						$ 11.9	$ 13.8	36.0	47.6
Income (expense) related to net adjustments to estimated fair value of liability for earnout obligations						$ (17.0)	$ 29.1	$ (3.1)	$ 60.2
Number of companies acquired						41	29	82	74	776
Aggregate amount of maximum earnout obligations related to acquisitions						$ 1,723.1		$ 1,723.1		$ 1,723.1
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet						823.5		823.5		823.5
Aggregate amount of earnout obligation expected settlement in cash or stock at option						557.9		557.9		557.9
Aggregate amount of earnout obligation expected settlement in cash						265.6		265.6		265.6
Goodwill						9,539.9		9,539.9		9,539.9
Expiration lists						6,774.6		6,774.6		6,774.6
Non-compete agreements						11.9		11.9		11.9
Trade names						37.5		37.5		37.5
Total revenues						3,881.5	$ 3,646.1	12,505.5	$ 11,346.0
Expiration Lists
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes						6,641.6		6,641.6		6,641.6
Non-Compete Agreements
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes						9.6		9.6		9.6
Trade Names
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes						37.5		37.5		37.5
Brokerage
Business Acquisition [Line Items]
Write-off of amortizable intangible assets						2.4	$ 5.4	43.0	$ 19.4
Brokerage Management
Business Acquisition [Line Items]
Goodwill						9,539.9		9,539.9		9,539.9
Expiration lists						6,774.6		6,774.6		6,774.6
Non-compete agreements						$ 11.9		$ 11.9		$ 11.9
Minimum
Business Acquisition [Line Items]
Business combination, earnout payable evaluation period								2 years
Minimum \| Expiration Lists
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years						2 years		2 years		2 years
Minimum \| Non-Compete Agreements
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years						2 years		2 years		2 years
Minimum \| Trade Names
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years						2 years		2 years		2 years
Maximum
Business Acquisition [Line Items]
Business combination, earnout payable evaluation period								3 years
Maximum \| Expiration Lists
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years						15 years		15 years		15 years
Maximum \| Non-Compete Agreements
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years						6 years		6 years		6 years
Maximum \| Trade Names
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years						15 years		15 years		15 years
AssuredPartners, Inc
Business Acquisition [Line Items]
Gross consideration	$ 13,800.0
Cash raised through follow-on common stock offering					$ 8,500.0
Number of employees \| employee	10,900
AssuredPartners, Inc \| Over-Allotment Option
Business Acquisition [Line Items]
Cash raised through follow-on common stock offering			$ 1,300.0
AssuredPartners, Inc \| Senior Notes
Business Acquisition [Line Items]
Cash borrowed from senior notes				$ 5,000.0
Business Acquisition
Business Acquisition [Line Items]
Expiration lists						$ 6,774.6		$ 6,774.6		$ 6,774.6
Non-compete agreements						11.9		11.9		11.9
Deferred tax liability						$ 728.3		728.3		$ 728.3
Annualized revenue of business acquisitions								3,427.7
Total revenues								504.9
Net earnings								(44.4)
Net earnings before interest, income taxes, depreciation, amortization and change in estimated acquisition earnout payables								$ 60.9
2025 Acquisitions \| Valuation, Market Approach \| Measurement Input, Discount Rate \| Minimum
Business Acquisition [Line Items]
Measurement input						0.050		0.050		0.050
2025 Acquisitions \| Valuation, Market Approach \| Measurement Input, Discount Rate \| Maximum
Business Acquisition [Line Items]
Measurement input						0.175		0.175		0.175
2025 Acquisitions \| Valuation, Income Approach \| Measurement Input, Discount Rate \| Minimum
Business Acquisition [Line Items]
Measurement input						0.081		0.081		0.081
2025 Acquisitions \| Valuation, Income Approach \| Measurement Input, Discount Rate \| Maximum
Business Acquisition [Line Items]
Measurement input						0.090		0.090		0.090
2024 Acquisitions \| Valuation, Market Approach \| Measurement Input, Long-term Revenue Growth Rate \| Minimum
Business Acquisition [Line Items]
Measurement input						0.030		0.030		0.030
2024 Acquisitions \| Valuation, Market Approach \| Measurement Input, Long-term Revenue Growth Rate \| Maximum
Business Acquisition [Line Items]
Measurement input						0.041		0.041		0.041
2024 Acquisitions \| Valuation, Income Approach \| Minimum
Business Acquisition [Line Items]
Attrition rate								5.00%
2024 Acquisitions \| Valuation, Income Approach \| Maximum
Business Acquisition [Line Items]
Attrition rate								12.00%
2024 Acquisitions \| Valuation, Income Approach \| Measurement Input, Long-term Revenue Growth Rate \| Minimum
Business Acquisition [Line Items]
Measurement input						0.095		0.095		0.095
2024 Acquisitions \| Valuation, Income Approach \| Measurement Input, Long-term Revenue Growth Rate \| Maximum
Business Acquisition [Line Items]
Measurement input						0.120		0.120		0.120
Woodruff Sawyer & Co April 10, 2025 (WSC)
Business Acquisition [Line Items]
Gross consideration		$ 1,200.0
Number of employees \| employee		600
Goodwill						$ 811.9		$ 811.9		$ 811.9
Expiration lists						459.2		459.2		459.2
Non-compete agreements						0.0		0.0		0.0
Trade names						$ 8.4		$ 8.4		$ 8.4
Woodruff Sawyer & Co April 10, 2025 (WSC) \| United States
Business Acquisition [Line Items]
Number of offices operating \| office		14
Woodruff Sawyer & Co April 10, 2025 (WSC) \| United Kingdom
Business Acquisition [Line Items]
Number of offices operating \| office		1