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Acquisitions of Businesses - Narrative on acquisitions of subsidiaries (Details) - USD ($) $ in Millions |  | 3 Months Ended | 12 Months Ended
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Jul. 03, 2023 | Dec. 31, 2024 | Dec. 31, 2022 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Business Acquisitions [Line Items] |  |  |  |  |  |
Cash paid at purchase |  |  |  | $ 9 | $ 234 | $ 10
Crop Risk Services |  |  |  |  |  |
Business Acquisitions [Line Items] |  |  |  |  |  |
Cash paid at purchase | $ 234 |  |  |  |  |
Net tangible assets acquired, at fair value | 24 |  |  |  |  |
Acquisition costs incurred | 3 |  |  |  |  |
Goodwill acquired during period | 85 |  |  |  | $ 85 |
Goodwill deductible for tax purposes | 79 |  |  |  |  |
Crop Risk Services | Customer relationships |  |  |  |  |  |
Business Acquisitions [Line Items] |  |  |  |  |  |
Intangible assets acquired | 124 |  |  |  |  |
Finite-lived intangible assets useful life |  | 14 years |  | 14 years |  |
Crop Risk Services | Crop Insurance Contract, Crop Year 2022 |  |  |  |  |  |
Business Acquisitions [Line Items] |  |  |  |  |  |
Gross written premiums | $ 1,200 |  |  |  |  |
Insurance Agency 2024 |  |  |  |  |  |
Business Acquisitions [Line Items] |  |  |  |  |  |
Cash paid at purchase |  | $ 5 |  |  |  |
Business acquisition, consideration transferred |  | 6 |  |  |  |
Consulting Company |  |  |  |  |  |
Business Acquisitions [Line Items] |  |  |  |  |  |
Cash paid at purchase |  | $ 4 |  |  |  |
Insurance Agency 2022 |  |  |  |  |  |
Business Acquisitions [Line Items] |  |  |  |  |  |
Cash paid at purchase |  |  | $ 10 |  |  |
Business acquisition, consideration transferred |  |  | $ 12 |  |  |

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- Definition Amount of direct costs of the business combination including legal, accounting, and other costs incurred to consummate the business acquisition. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 805 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479907/805-20-50-5 + Details
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- Definition The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479581/805-30-50-1 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 30 -Paragraph 8 -SubTopic 30 -Topic 805 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479637/805-30-30-8 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -SubTopic 30 -Topic 805 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479581/805-30-50-1 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 30 -Paragraph 7 -SubTopic 30 -Topic 805 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479637/805-30-30-7 + Details
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- Definition The amount of identifiable intangible assets recognized as of the acquisition date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479303/805-10-55-37 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479907/805-20-50-1 + Details
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- Definition Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479303/805-10-55-37 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479907/805-20-50-1 + Details
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- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 24 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482548/350-20-55-24 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 350 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482573/350-20-50-1 + Details
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- Definition The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 805 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479581/805-30-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-13 + Details
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