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Transactions With Related Parties (Details) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2022
Related Party Transaction [Line Items] |  |  |  |
Net premiums written | $ 4,085 | $ 3,424 |  |
Net premiums earned | 3,422 | 2,883 |  |
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses | 7,509 | 6,612 | $ 7,064 | $ 6,564
Reinsurance balances payable | 2,497 |  | 2,000 |
Operating affiliates | Premia |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Net premiums written |  | 75 |  |
Net premiums earned |  | 75 |  |
Funds held asset | 144 |  | 158 |
Operating affiliates | Somers |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Net premiums written | 219 | $ 155 |  |
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses | 1,400 |  | 1,300 |
Reinsurance balances payable | $ 584 |  | $ 475 |

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- Definition Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 235 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17(Column E)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477965/944-235-S99-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(13)(c)) -SubTopic 220 -Topic 942 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478524/942-220-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(1)) -SubTopic 220 -Topic 944 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 + Details
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