Investments - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) security fund manager	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) security
Schedule of Investments [Line Items]
Number of outside managers managing investment portfolio | manager	3
Accrued investment income	$ 72		$ 71
Number of securities with unrealized losses greater than 10% of book value for 12 months or more | security	458		409
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more	$ 224		$ 200
Assets held-in-trust	143		234
Securities purchased with credit deterioration	0	$ 0
Disposal Group, Held-for-sale, Not Discontinued Operations | Sound Point Agreement
Schedule of Investments [Line Items]
Transaction commitment, new and transitioned investments	1,000
AGL Subsidiaries
Schedule of Investments [Line Items]
Assets held-in-trust	$ 1,144		$ 1,154
AGAS
Schedule of Investments [Line Items]
Funds accounted for as CIVs | fund	3
Total number of investments | fund	8
Future Equity Investments
Schedule of Investments [Line Items]
Investments, authorized amount to invest	$ 1,500
Investments, fair value disclosure	803
Unfunded commitment	743
Unfunded commitment, committed for specific funds	324
Investments, including distributed gains, authorized amount to invest	162
Future Equity Investments | AGL Subsidiaries
Schedule of Investments [Line Items]
Investments, authorized amount to invest	912
Authorized amount to invest, excluding distributed gains	750
Equity in Earnings (Losses) of Investees | AGAS
Schedule of Investments [Line Items]
Investments, fair value disclosure	632
Long-term purchase commitment, amount	772
Funded amount	$ 574