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Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022 | Dec. 31, 2022 | Dec. 31, 2010
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |
Unusual or Infrequent Item, or Both, Net of Insurance Proceeds | $ 94 | $ 114 | $ 214 | $ 171 |  |
Total pretax (favorable) unfavorable development | 13 | (17) | 44 | (2) |  |
Retroactive reinsurance benefit recognized | 15 | 17 | 38 | 40 |  |
Cumulative amounts ceded under AEP Loss Portfolio Transfer | 3,500 |  | 3,500 |  | $ 3,500 |
Hurricane Ian |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |
Unusual or Infrequent Item, or Both, Net of Insurance Proceeds |  |  |  | 87 |  |
Corporate & Other |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |
Total pretax (favorable) unfavorable development | 20 | $ 0 | 55 | $ 64 |  |
Asbestos and Environmental Reserves |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |
Net A&EP claim and allocated claim adjustment expense reserves ceded to NICO |  |  |  |  |  | $ 1,600
Aggregate limit under A&EP Loss Portfolio Transfer |  |  |  |  |  | 4,000
A&EP claim and allocated claim adjustment expense reserves ceded under existing third party reinsurance contracts transferred to NICO under A&EP Loss Portfolio Transfer |  |  |  |  |  | 1,200
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer |  |  |  |  |  | 2,000
Net reinsurance receivables transferred to NICO under A&EP Loss Portfolio Transfer |  |  |  |  |  | 215
Total consideration paid to NICO under AEP Loss Portfolio Transfer |  |  |  |  |  | $ 2,200
Deferred reinsurance benefit yet to be recognized | 388 |  | 388 |  | $ 425 |
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer | $ 2,300 |  | $ 2,300 |  |  |

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