Investments - Internally Managed Investment Portfolio (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	$ 6,006	$ 6,307
Fixed-maturity securities, trading	221	318
Short-term investments, at fair value	1,717	1,661
Other invested assets	882	829
Total investments	$ 8,826	$ 9,115
Fixed-maturity investments, non-investment grade, percent	9.40%	9.20%
Sound Point Capital Management, LP
Debt and Equity Securities, FV-NI [Line Items]
Equity method investments	$ 413	$ 429
Total investments	641	631
Externally managed
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	5,298	5,372
Loss Mitigation Securities
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	465	459
Other
Debt and Equity Securities, FV-NI [Line Items]
Estimated fair value	243	476
Alternative Investment
Debt and Equity Securities, FV-NI [Line Items]
Equity method investments	462	394
Other
Debt and Equity Securities, FV-NI [Line Items]
Other invested assets	$ 7	$ 6