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Acquisitions and Dispositions of Businesses - Narrative (Details) shares in Millions |  |  | 3 Months Ended | 6 Months Ended |  |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 25, 2024 USD ($) employee shares | Mar. 31, 2024 USD ($) | Jun. 30, 2024 USD ($) acquisition | Jun. 30, 2023 acquisition | Jun. 30, 2024 USD ($) acquisition | Jun. 30, 2023 acquisition | Jun. 18, 2024 | Jun. 13, 2024 | May 31, 2024 | May 02, 2024 | Apr. 26, 2024 | Apr. 03, 2024 | Dec. 31, 2023 USD ($) | Nov. 30, 2023 | Aug. 30, 2023 | Jun. 22, 2023
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of business acquired under business combination | acquisition |  |  | 8 | 1 | 8 | 1 |  |  |  |  |  |  |  |  |  |
Issuance of debt |  | $ 6,000,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from long-term lines of credit | $ 2,000,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill |  |  | $ 15,281,000,000 |  | $ 15,281,000,000 |  |  |  |  |  |  |  | $ 8,414,000,000 |  |  |
Intangible assets, net |  |  | 6,794,000,000 |  | 6,794,000,000 |  |  |  |  |  |  |  | $ 234,000,000 |  |  |
Extinguishment of debt |  |  | 6,000,000 |  | 6,000,000 |  |  |  |  |  |  |  |  |  |  |
NFP Acquisition |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of colleagues (more than) | employee | 7,700 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Southern Insurance Agency, L.L.C., |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  | 100.00% |  |  |  |  |  |  |  |  |
Sean Barrett Bloodstock Insurance Limited, |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  | 100.00% |  |  |  |  |  |  |  |
Walden Wealth Partners LLC., |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  |  | 100.00% |  |  |  |  |  |  |
Morley Agency, Inc., |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  |  | 100.00% |  |  |  |  |  |  |
Honest Employment Law Practice Ltd., |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  |  |  | 100.00% |  |  |  |  |  |
Novabrok |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  |  |  |  | 100.00% |  |  |  |  |
NFP Acquisition |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired | 100.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total consideration | $ 9,100,000,000 |  |  |  | 9,129,000,000 |  |  |  |  |  |  |  |  |  |  |
Cash | $ 3,200,000,000 |  |  |  | 3,247,000,000 |  |  |  |  |  |  |  |  |  |  |
Number of shares issued for acquisition (up to) | shares | 19 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity interest issued or issuable, value | $ 5,900,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill |  |  | 6,953,000,000 |  | $ 6,953,000,000 |  |  |  |  |  |  |  |  |  |  |
Weighted average useful life |  |  |  |  | 19 years |  |  |  |  |  |  |  |  |  |  |
Intangible assets, net |  |  | 6,500,000,000 |  | $ 6,500,000,000 |  |  |  |  |  |  |  |  |  |  |
Acquisition related costs |  |  | $ 79,000,000 |  | $ 90,000,000 |  |  |  |  |  |  |  |  |  |  |
NFP Acquisition | Customer Relationships |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average useful life |  |  |  |  | 20 years |  |  |  |  |  |  |  |  |  |  |
NFP Acquisition | Tradenames |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average useful life |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |  |  |
NFP Acquisition | Technology and other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average useful life |  |  |  |  | 7 years |  |  |  |  |  |  |  |  |  |  |
Global Insurance Brokers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |  |  |
Gi&Bi S.r.l |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |
N. Goddard Seguros |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |
2023 Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00%

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