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v3.25.1

Supplemental Disclosures of Cash Flow Information - Additional Information (Detail) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jan. 31, 2025 | Mar. 31, 2025 | Mar. 31, 2024 | Dec. 31, 2024 | Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Stock issuance |  | $ 1,252.1 |  |  |
Proceeds from issuance of common stock |  | 1,334.8 | $ 52.0 |  |
Money Market Accounts [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Total cash and cash equivalents, restricted cash and fiduciary cash |  | 17,044.9 | 2,116.1 |  |
Proceeds from AssuredPartners financing |  | 13,500.0 |  |  |
Money Market Accounts [Member] | Investment Income [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Increases dividend income |  | 154.2 |  |  |
Proceeds from AssuredPartners financing |  | 142.6 |  |  |
Dividend income |  | $ 247.6 | $ 93.4 |  |
Money Market Accounts [Member] | Over-Allotment Option [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Proceeds from issuance of common stock | $ 1,300.0 |  |  |  |
Qualified Contributory Savings and Thrift 401(k) Plan [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Matching contributions by employer, percentage |  | 100.00% |  |  |
Percentage of eligible compensation for matching contributions by employer |  | 5.00% | 5.00% |  |
Matching contributions vesting schedule |  | 5 years |  |  |
Contribution expense to plan |  | $ 29.9 | $ 26.1 |  |
Employer match on eligible compensation |  |  |  | 5.00% | 5.00%

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