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Investments - Internally Managed Investment Portfolio (Details) - USD ($) $ in Millions | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | $ 8,156 | $ 8,202
Fixed-maturity securities, trading | 174 | 0
Short-term investments, at fair value | 585 | 1,225
Other invested assets | 152 | 181
Total investments | $ 9,067 | $ 9,608
BIG |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed-maturity investments, non-investment grade, percent | 7.30% | 7.50%
Not Internally Rated |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed-maturity investments, non-investment grade, percent | 7.20% | 0.90%
Externally managed |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | $ 6,316 | $ 6,843
Loss mitigation securities and other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | 789 | 818
AssuredIM managed |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | 537 | 541
Recovery Bonds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | 514 | 0
Equity method investments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other invested assets | 145 | 169
Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other invested assets | $ 7 | $ 12

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