Investments - Internally Managed Investment Portfolio (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	$ 6,091	$ 6,307
Fixed-maturity securities, trading	272	318
Short-term investments, at fair value	1,649	1,661
Other invested assets	875	829
Total investments	$ 8,887	$ 9,115
Fixed-maturity investments, non-investment grade, percent	9.50%	9.20%
Sound Point Capital Management, LP
Debt and Equity Securities, FV-NI [Line Items]
Equity method investments	$ 417	$ 429
Total investments	636	631
Externally managed
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	5,383	5,372
Loss Mitigation Securities
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	464	459
Other
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	244	476
Alternative Investment
Debt and Equity Securities, FV-NI [Line Items]
Equity method investments	451	394
Other
Debt and Equity Securities, FV-NI [Line Items]
Other invested assets	$ 7	$ 6