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Investments - Internally Managed Investment Portfolio (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | $ 6,869 | $ 7,119
Fixed-maturity securities, trading | 300 | 303
Short-term investments, at fair value | 1,273 | 810
Other invested assets | 140 | 133
Total investments | 8,582 | 8,365
Externally managed |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | 5,498 | 5,519
Loss mitigation securities and other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | 696 | 705
AssuredIM managed |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | 539 | 537
Recovery Bonds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | $ 136 | $ 358
BIG |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed-maturity investments, non-investment grade, percent | 7.50% | 7.40%
Not Internally Rated |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed-maturity investments, non-investment grade, percent | 2.90% | 5.90%
Equity method investments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other invested assets | $ 122 | $ 123
Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other invested assets | $ 18 | $ 10

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