v3.25.4

Summary of Significant Accounting Policies (Narrative) (Details) | 12 Months Ended
--- | ---
Dec. 31, 2025 USD ($) segment | Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Number of business segments | segment | 2 |  |
Restricted cash, current | $ 553,000,000 | $ 455,000,000 |
Equity method investment, Lag period | 3 months |  |
Investment income | $ 34,000,000 | 12,000,000 | $ 5,000,000
Indefinite lived identified intangible assets | 0 | 0 |
Capitalized computer software costs | 466,000,000 | 474,000,000 |
Accumulated amortization | 2,300,000,000 | 2,100,000,000 |
Liability for errors and omissions | 379,000,000 | 391,000,000 |
Net uncollected premiums and claims and related payables | 14,600,000,000 | 15,100,000,000 |
Mc Griff Insurance Services L L C |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Increase due to acquisition |  | 465,000,000 |
Risk and Insurance Services |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Interest income, fiduciary assets | 403,000,000 | 497,000,000 | $ 453,000,000
Accounts Payable and Accrued Liabilities |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Liabilities for errors and omissions, current | $ 91,000,000 | $ 86,000,000 |
Office Space | Lease Obligations | Lease Concentration Risk |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Concentration risk (as a percent) | 98.00% |  |
Minimum | Customer Lists |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Intangible assets, useful life | 10 years |  |
Minimum | Furniture and equipment |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Property, plant and equipment, useful life | 3 years |  |
Minimum | Building |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Property, plant and equipment, useful life | 30 years |  |
Minimum | Software Development |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Property, plant and equipment, useful life | 3 years |  |
Maximum | Customer Lists |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Intangible assets, useful life | 15 years |  |
Maximum | Furniture and equipment |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Property, plant and equipment, useful life | 10 years |  |
Maximum | Building |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Property, plant and equipment, useful life | 40 years |  |
Maximum | Software Development |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Property, plant and equipment, useful life | 10 years |  |

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