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Investments and Cash - Narrative (Details) £ in Millions, $ in Millions |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jul. 01, 2023 USD ($) | Dec. 31, 2024 USD ($) fund security | Dec. 31, 2022 USD ($) | Feb. 27, 2025 USD ($) | Feb. 27, 2025 GBP (£) | Dec. 31, 2023 USD ($) security
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Fixed-maturity investments, non-investment grade, not rated, percent |  | 12.60% |  |  |  | 9.20%
Fixed-maturity securities, available-for-sale |  | $ 6,369 |  |  |  | $ 6,307
Accounted for as consolidated investment vehicles | fund |  | 1 |  |  |  |
Accrued investment income |  | $ 64 |  |  |  | $ 71
Number of securities with unrealized losses greater than 10% of book value for 12 months or more | security |  | 438 |  |  |  | 409
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more |  | $ 223 |  |  |  | $ 200
Assets held-in-trust |  | 79 |  |  |  | 234
Non-income producing investments |  | 42 |  |  |  | 0
Fixed-maturity securities, trading, at fair value |  | 147 |  |  |  | 318
Purchased with credit deterioration, amount at purchase price |  |  | $ 22 |  |  |
Securities purchased with credit deterioration, amount at par value |  |  | 31 |  |  |
Allowance for credit loss at acquisition date |  |  | 2 |  |  |
Discount attributable to other factors |  |  | $ 7 |  |  |
Contingent Value Instruments |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Fixed-maturity securities, trading, at fair value |  | 123 |  |  |  |
Loss mitigation securities |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Fixed-maturity securities, available-for-sale |  | 479 |  |  |  | 459
Collateralized Loan Obligation Equity Tranches |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Fixed-maturity securities, available-for-sale |  | 277 |  |  |  | 13
Sound Point |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Equity method investments |  | $ 418 |  |  |  | 429
Useful life |  | 5 years 6 months |  |  |  |
Disposal Group, Held-for-Sale, Not Discontinued Operations | Sound Point Agreement |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Investment management commitment | $ 1,000 | $ 1,000 |  |  |  |
Assured Guaranty Subsidiaries |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Assets held-in-trust |  | 1,135 |  |  |  | 1,154
Debt Securities Through A Facility | Subsequent Event |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Purchase commitment, debt securities |  |  |  | $ 139 | £ 110 |
Alternative Investment | Consolidated investment vehicles |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Equity method investments |  | 33 |  |  |  | $ 305
Alternative Investment | Future Equity Investments |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Fair value of investment |  | 884 |  |  |  |
Authorized amount to invest |  | 1,500 |  |  |  |
Unfunded commitment |  | 610 |  |  |  |
Sound Point |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Indefinite-lived intangible assets |  | 245 |  |  |  |
Finite-lived intangible assets |  | 31 |  |  |  |
Other |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |
Fair value of investment |  | $ 508 |  |  |  |

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