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Business Combinations - Additional Information (Detail) $ in Millions |  | 3 Months Ended
--- | --- | ---
Aug. 18, 2025 USD ($) segment | Mar. 31, 2026 USD ($) acquisition | Mar. 31, 2025 USD ($) acquisition
Business Combination [Line Items] |  |  |
Accretion of the discount on acquisition |  | $ 14 | $ 13
Income (expense) related to net adjustments to estimated fair value of liability for earnout obligations |  | $ (3) | $ (3)
Number of companies acquired | acquisition |  | 51 | 28
Aggregate amount of maximum earnout obligations related to acquisitions |  | $ 1,385 |
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet |  | 651 |
Aggregate amount of earnout obligation expected settlement in cash or stock at option |  | 511 |
Aggregate amount of earnout obligation expected settlement in cash |  | 140 |
Goodwill |  | 201 |
Expiration lists |  | 162 |
Non-compete agreements |  | 13 |
Total revenues |  | 4,765 | $ 3,740
Expiration Lists |  |  |
Business Combination [Line Items] |  |  |
Business acquisition not deductible for income tax purposes |  | 137 |
Non-Compete Agreements |  |  |
Business Combination [Line Items] |  |  |
Business acquisition not deductible for income tax purposes |  | 13 |
Brokerage |  |  |
Business Combination [Line Items] |  |  |
Write-off of amortizable intangible assets |  | 1 | $ 41
Brokerage Management |  |  |
Business Combination [Line Items] |  |  |
Goodwill |  | 201 |
Expiration lists |  | 162 |
Non-compete agreements |  | $ 13 |
Minimum |  |  |
Business Combination [Line Items] |  |  |
Business combination, earnout payable evaluation period |  | 2 years |
Minimum | Expiration Lists |  |  |
Business Combination [Line Items] |  |  |
Estimated useful lives of intangibles assets, years |  | 2 years |
Minimum | Non-Compete Agreements |  |  |
Business Combination [Line Items] |  |  |
Estimated useful lives of intangibles assets, years |  | 2 years |
Minimum | Trade Names |  |  |
Business Combination [Line Items] |  |  |
Estimated useful lives of intangibles assets, years |  | 2 years |
Maximum |  |  |
Business Combination [Line Items] |  |  |
Business combination, earnout payable evaluation period |  | 3 years |
Maximum | Expiration Lists |  |  |
Business Combination [Line Items] |  |  |
Estimated useful lives of intangibles assets, years |  | 15 years |
Maximum | Non-Compete Agreements |  |  |
Business Combination [Line Items] |  |  |
Estimated useful lives of intangibles assets, years |  | 6 years |
Maximum | Trade Names |  |  |
Business Combination [Line Items] |  |  |
Estimated useful lives of intangibles assets, years |  | 15 years |
AssuredPartners, Inc |  |  |
Business Combination [Line Items] |  |  |
Gross consideration | $ 13,800 |  |
Number of employees | segment | 10,900 |  |
Business combination, initial accounting incomplete, adjustment of goodwill |  | $ 220 |
AssuredPartners, Inc | Expiration Lists |  |  |
Business Combination [Line Items] |  |  |
Business combination, initial accounting incomplete, adjustment of intangible assets |  | (222) |
AssuredPartners, Inc | Trade Names |  |  |
Business Combination [Line Items] |  |  |
Business combination, initial accounting incomplete, adjustment of intangible assets |  | 2 |
Business Acquisition |  |  |
Business Combination [Line Items] |  |  |
Expiration lists |  | 162 |
Non-compete agreements |  | 13 |
Deferred tax liability |  | 47 |
Annualized revenue of business acquisitions |  | 59 |
Total revenues |  | 7 |
Net earnings |  | (3) |
Net earnings before interest, income taxes, depreciation, amortization and change in estimated acquisition earnout payables |  | $ 0 |
2026 Acquisitions | Valuation, Market Approach | Measurement Input, Discount Rate | Minimum |  |  |
Business Combination [Line Items] |  |  |
Measurement input |  | 0.050 |
2026 Acquisitions | Valuation, Market Approach | Measurement Input, Discount Rate | Maximum |  |  |
Business Combination [Line Items] |  |  |
Measurement input |  | 0.150 |
2026 Acquisitions | Valuation, Income Approach | Measurement Input, Discount Rate |  |  |
Business Combination [Line Items] |  |  |
Measurement input |  | 0.090 |
2025 Acquisitions | Valuation, Market Approach | Measurement Input, Long-term Revenue Growth Rate | Minimum |  |  |
Business Combination [Line Items] |  |  |
Measurement input |  | 0.030 |
2025 Acquisitions | Valuation, Income Approach | Minimum |  |  |
Business Combination [Line Items] |  |  |
Attrition rate |  | 5.00% |
2025 Acquisitions | Valuation, Income Approach | Maximum |  |  |
Business Combination [Line Items] |  |  |
Attrition rate |  | 10.00% |
2025 Acquisitions | Valuation, Income Approach | Measurement Input, Long-term Revenue Growth Rate | Minimum |  |  |
Business Combination [Line Items] |  |  |
Measurement input |  | 0.090 |
2025 Acquisitions | Valuation, Income Approach | Measurement Input, Long-term Revenue Growth Rate | Maximum |  |  |
Business Combination [Line Items] |  |  |
Measurement input |  | 0.100 |

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