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Investments - Internally Managed Investment Portfolio (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	$ 6,780	$ 8,202
Fixed-maturity securities, trading	393	0
Short-term investments, at fair value	1,177	1,225
Other invested assets	130	181
Total investments	8,480	9,608
Externally managed
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	5,456	6,843
Loss mitigation securities and other
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	744	818
AssuredIM managed
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	516	541
Recovery Bonds
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	$ 64	$ 0
BIG
Debt and Equity Securities, FV-NI [Line Items]
Fixed-maturity investments, non-investment grade, percent	8.30%	7.50%
Not Internally Rated
Debt and Equity Securities, FV-NI [Line Items]
Fixed-maturity investments, non-investment grade, percent	1.80%	0.90%
Equity method investments
Debt and Equity Securities, FV-NI [Line Items]
Other invested assets	$ 120	$ 169
Other
Debt and Equity Securities, FV-NI [Line Items]
Other invested assets	$ 10	$ 12

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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