Investments and Cash - Investment Portfolio Carrying Value (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities, available-for-sale, at fair value, net of allowance for credit loss	$ 6,307	$ 7,119
Fixed-maturity securities, trading, at fair value	318	303
Short-term investments, at fair value	1,661	810
Other invested assets	829	133
Total investments	9,115	8,365
Externally managed
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities, available-for-sale, at fair value, net of allowance for credit loss	5,372	5,824
Externally managed | Internal
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities, available-for-sale, at fair value, net of allowance for credit loss	318	305
Puerto Rico, New Recovery Bonds
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities, available-for-sale, at fair value, net of allowance for credit loss	14	358
Other
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities, available-for-sale, at fair value, net of allowance for credit loss	462	431
Other | Assured IM
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities, available-for-sale, at fair value, net of allowance for credit loss	223	232
Loss Mitigation Securities
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities, available-for-sale, at fair value, net of allowance for credit loss	$ 459	$ 506
BIG
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities rated as BIG	7.80%	7.40%
Not Internally Rated
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities rated as BIG	1.40%	5.90%
Sound Point
Schedule of Cost-method Investments [Line Items]
Other invested assets	$ 429	$ 0
Other
Schedule of Cost-method Investments [Line Items]
Other invested assets	394	123
Other
Schedule of Cost-method Investments [Line Items]
Other invested assets	$ 6	$ 10