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Claim and Claim Adjustment Expense Reserves (Gross and Net Carried Claim and Claim Adjustment Expense Reserves) (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | --- | --- | ---
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | $ 8,402 | $ 7,738 |  |
Gross IBNR Reserves | 16,574 | 15,566 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 24,976 | 23,304 | $ 22,120 | $ 21,269
Net Case Reserves | 6,207 | 5,663 |  |
Net IBNR Reserves | 13,056 | 12,500 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 19,263 | 18,163 | $ 16,929 | $ 16,300
Specialty |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 2,023 | 1,604 |  |
Gross IBNR Reserves | 5,403 | 5,527 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 7,426 | 7,131 |  |
Net Case Reserves | 1,697 | 1,392 |  |
Net IBNR Reserves | 4,282 | 4,524 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 5,979 | 5,916 |  |
Commercial |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 3,690 | 3,291 |  |
Gross IBNR Reserves | 7,646 | 6,812 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 11,336 | 10,103 |  |
Net Case Reserves | 3,135 | 2,878 |  |
Net IBNR Reserves | 6,804 | 6,143 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 9,939 | 9,021 |  |
International |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 876 | 864 |  |
Gross IBNR Reserves | 2,044 | 1,845 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 2,920 | 2,709 |  |
Net Case Reserves | 741 | 708 |  |
Net IBNR Reserves | 1,675 | 1,568 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 2,416 | 2,276 |  |
Life & Group |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 572 | 626 |  |
Gross IBNR Reserves | 50 | 49 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 622 | 675 |  |
Net Case Reserves | 514 | 556 |  |
Net IBNR Reserves | 27 | 26 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 541 | 582 |  |
Corporate & Other |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 1,241 | 1,353 |  |
Gross IBNR Reserves | 1,431 | 1,333 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 2,672 | 2,686 |  |
Net Case Reserves | 120 | 129 |  |
Net IBNR Reserves | 268 | 239 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | $ 388 | $ 368 |  |

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