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Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Gross and Net Carried Claim and Claim Adjustment Expense Reserves) (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | --- | ---
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | $ 10,555 | $ 10,694 |  |
Gross IBNR Reserves | 13,619 | 12,012 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 24,174 | 22,706 | $ 21,720 | $ 21,984
Net Case Reserves | 8,369 | 8,930 |  |
Net IBNR Reserves | 10,836 | 9,771 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 19,205 | 18,701 | $ 17,885 | $ 17,965
Specialty |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 1,578 | 1,567 |  |
Gross IBNR Reserves | 4,855 | 4,181 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 6,433 | 5,748 |  |
Net Case Reserves | 1,338 | 1,410 |  |
Net IBNR Reserves | 3,927 | 3,488 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 5,265 | 4,898 |  |
Commercial |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 3,184 | 3,215 |  |
Gross IBNR Reserves | 5,706 | 5,035 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 8,890 | 8,250 |  |
Net Case Reserves | 2,850 | 2,885 |  |
Net IBNR Reserves | 5,215 | 4,590 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 8,065 | 7,475 |  |
International |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 859 | 892 |  |
Gross IBNR Reserves | 1,421 | 1,199 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 2,280 | 2,091 |  |
Net Case Reserves | 744 | 777 |  |
Net IBNR Reserves | 1,196 | 1,045 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 1,940 | 1,822 |  |
Life & Group |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 3,383 | 3,406 |  |
Gross IBNR Reserves | 371 | 337 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 3,754 | 3,743 |  |
Net Case Reserves | 3,291 | 3,298 |  |
Net IBNR Reserves | 350 | 317 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | 3,641 | 3,615 |  |
Corporate & Other |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Gross Case Reserves | 1,551 | 1,614 |  |
Gross IBNR Reserves | 1,266 | 1,260 |  |
Total Gross Carried Claim and Claim Adjustment Expense Reserves | 2,817 | 2,874 |  |
Net Case Reserves | 146 | 560 |  |
Net IBNR Reserves | 148 | 331 |  |
Total Net Carried Claim and Claim Adjustment Expense Reserves | $ 294 | $ 891 |  |

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