Investments - Additional Information (Details) £ in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2025 USD ($) security	Mar. 31, 2024 USD ($)	Mar. 31, 2025 GBP (£) security	Dec. 31, 2024 USD ($) security
Schedule of Investments [Line Items]
Fixed-maturity investments, non-investment grade, percent	12.30%		12.30%	12.60%
Estimated Fair Value	$ 6,415			$ 6,369
Alternative investment	892
Accrued investment income	$ 67			$ 64
Number of securities with unrealized losses greater than 10% of book value for 12 months or more | security	371		371	438
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more	$ 202			$ 223
Assets held-in-trust	82			79
Fixed-maturity securities, trading	137			147
Securities purchased with credit deterioration	0	$ 0
Insured Financial Obligations, Loss Mitigation Securities
Schedule of Investments [Line Items]
Estimated Fair Value	497			479
Collateralized Loan Obligation Equity Tranches
Schedule of Investments [Line Items]
Estimated Fair Value	240			277
Consolidated Investment Vehicles | Alternative Investment
Schedule of Investments [Line Items]
Equity method investments	39			33
Contingent Value Instruments
Schedule of Investments [Line Items]
Fixed-maturity securities, trading	115
CLOs
Schedule of Investments [Line Items]
Estimated Fair Value	542			611
Financial Instrument, Other
Schedule of Investments [Line Items]
Investments, fair value disclosure	549
Sound Point Capital Management, LP
Schedule of Investments [Line Items]
Equity method investments	411			418
AGL Subsidiaries
Schedule of Investments [Line Items]
Assets held-in-trust	1,079			$ 1,135
Future Equity Investments
Schedule of Investments [Line Items]
Alternative investment	892
Investments, authorized amount to invest	1,500
Future Equity Investments | Alternative Investment
Schedule of Investments [Line Items]
Investments, unfunded commitment	608
Future Equity Investments | Sound Point Capital Management, LP
Schedule of Investments [Line Items]
Investments, authorized amount to invest	1,000
Debt Securities Through A Facility
Schedule of Investments [Line Items]
Purchase commitment, debt securities	$ 142		£ 110