Investments - Additional Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($) security	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) security manager fund	Jun. 30, 2023 USD ($)	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	$ 66		$ 66		$ 71
Number of securities with unrealized losses greater than 10% of book value for 12 months or more | security	478		478		409
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more	$ 234		$ 234		$ 200
Assets held-in-trust	74		74		234
Sales	129	$ 239	488	$ 694
Securities purchased with credit deterioration	0	$ 0	0	$ 0
AGL Subsidiaries
Schedule of Investments [Line Items]
Assets held-in-trust	1,152		1,152		$ 1,154
Future Equity Investments
Schedule of Investments [Line Items]
Investments, authorized amount to invest	1,500		1,500
Unfunded commitment	734		734
Investments, fair value disclosure	810		810
Future Equity Investments | Sound Point Capital Management, LP
Schedule of Investments [Line Items]
Investments, authorized amount to invest	$ 1,000		$ 1,000