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v3.24.3

Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Phantom) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023
Investment [Line Items] |  |  |  |  |
Investment expense | $ (1) | $ (1) | $ (4) | $ (4) |
Net investment income | 38 | 30 | 116 | 100 |
Standard & Poor's, B- Rating [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Investment Owned, at Fair Value | 421 |  | 421 |  | $ 482
Standard & Poor's, B- Rating [Member] | Mortgage-Backed Securities, Other |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Investment Owned, at Fair Value | 258 |  | 258 |  | 240
Standard & Poor's, B- Rating [Member] | Asset-backed Securities [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Investment Owned, at Fair Value | 154 |  | 154 |  | $ 232
Gains (losses) on securities held as of reporting date [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Other Investments Income | 9 | 0 | 15 | 6 |
Fixed Income Investments [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Gross Investment Income, Operating | 22 | 20 | 67 | 55 |
Short-Term [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Gross Investment Income, Operating | 4 | 5 | 14 | 16 |
Other Investments [Member] |  |  |  |  |
Investment [Line Items] |  |  |  |  |
Gross Investment Income, Operating | $ 14 | $ 6 | $ 35 | $ 28 |

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