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Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($) |  | 3 Months Ended | 12 Months Ended | 13 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Feb. 05, 2021 | Mar. 31, 2022 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Feb. 05, 2021 | Dec. 31, 2012 | Dec. 31, 2010
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |
Pretax (favorable) unfavorable premium development, excluding Life & Group |  |  | $ 48,000,000 | $ 48,000,000 | $ (32,000,000) |  |  |
Funds held under reinsurance agreements, liability | $ 690,000,000 |  | 3,400,000,000 | 3,600,000,000 |  | $ 690,000,000 |  |
Retroactive reinsurance agreement, maximum | 1,000,000,000 |  |  |  |  | 1,000,000,000 |  |
Reinsurance premiums paid | $ 697,000,000 |  |  |  |  | $ 64,000,000 |  |
Reinsurance, loss on uncollectible accounts in period, amount |  | $ 12,000,000 |  |  |  |  |  |
Securities held as collateral, at fair value |  |  | 298,000,000 |  |  |  |  |
Corporate & Other |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |
Pretax (favorable) unfavorable premium development, excluding Life & Group |  |  | 79,000,000 | 71,000,000 | 64,000,000 |  |  |
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 |  |  |  |  |  |  |  | $ 1,600,000,000
Aggregate limit under A&EP Loss Portfolio Transfer |  |  |  |  |  |  |  | 4,000,000,000
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 |  |  |  |  |  |  |  | 1,200,000,000
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer |  |  |  |  |  |  |  | 2,000,000,000
Net reinsurance receivables transferred to NICO under A&EP Loss Portfolio Transfer |  |  |  |  |  |  |  | 215,000,000
Total consideration paid to NICO under AEP Loss Portfolio Transfer |  |  |  |  |  |  | $ 2,200,000,000 | $ 2,200,000,000
Net A&EP adverse development before consideration of LPT |  |  | 103,000,000 | 86,000,000 | 92,000,000 |  |  |
Provision for uncollectible third-party reinsurance, released |  |  | 0 | 5,000,000 | $ 5,000,000 |  |  |
Cumulative amounts ceded under AEP Loss Portfolio Transfer |  |  | 3,700,000,000 | 3,600,000,000 |  |  |  |
Deferred reinsurance benefit yet to be recognized |  |  | 425,000,000 | $ 417,000,000 |  |  |  |
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer |  |  | 2,300,000,000 |  |  |  |  |
Excess Workers' Compensation LPT |  |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |  |
Funds held under reinsurance agreements, liability |  |  | $ 690,000,000 |  |  |  |  |

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- Definition Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, net of estimated reinsurance recoveries. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (cc) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-3 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-3 + Details
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