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Investments - Internally Managed Investment Portfolio (Details) - USD ($) $ in Millions | Jun. 30, 2022 | Dec. 31, 2021
--- | --- | ---
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | $ 7,396 | $ 8,202
Fixed-maturity securities, trading | 87 | 0
Short-term investments, at fair value | 863 | 1,225
Other invested assets | 150 | 181
Total investments | 8,496 | 9,608
Externally managed |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | 5,894 | 6,843
Loss mitigation securities and other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | 735 | 818
AssuredIM managed |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | 526 | 541
Recovery Bonds |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Estimated fair value | $ 241 | $ 0
BIG |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed-maturity investments, non-investment grade, percent | 7.40% | 7.50%
Not Internally Rated |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fixed-maturity investments, non-investment grade, percent | 4.10% | 0.90%
Equity method investments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other invested assets | $ 140 | $ 169
Other |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Other invested assets | $ 10 | $ 12

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