Investments - Additional Information (Details) £ in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024 USD ($) security	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) security fund manager	Sep. 30, 2023 USD ($)	Nov. 12, 2024 GBP (£)	Dec. 31, 2023 USD ($) security
Schedule of Investments [Line Items]
Number of outside managers managing investment portfolio | manager			3
Funds accounted for as CIVs | fund			3
Accrued investment income	$ 71		$ 71			$ 71
Number of securities with unrealized losses greater than 10% of book value for 12 months or more | security	317		317			409
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more	$ 149		$ 149			$ 200
Assets held-in-trust	77		77			234
Sales	87	$ 73	575	$ 767
Securities purchased with credit deterioration	0	$ 0	0	$ 0
AGL Subsidiaries
Schedule of Investments [Line Items]
Assets held-in-trust	1,176		1,176			$ 1,154
Future Equity Investments
Schedule of Investments [Line Items]
Unfunded commitment	690		690
Investments, fair value disclosure	848		848
Investments, authorized amount to invest	1,500		1,500
Future Equity Investments | Sound Point Capital Management, LP
Schedule of Investments [Line Items]
Investments, authorized amount to invest	$ 1,000		$ 1,000
Debt Securities Through A Facility | Subsequent Event
Schedule of Investments [Line Items]
Purchase commitment, debt securities | £					£ 80