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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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