Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
Premiums
Total premiums	$ 44,237	$ 39,916	[1]	$ 41,154	[1]
Total reinsurance recoveries
Total reinsurance recoveries	456	702		552
Short-duration contracts
Premiums
Direct	42,266	36,747		36,513
Assumed	303	416		335
Ceded	(277)	(265)		(148)
Total premiums	42,292	36,898		36,700
Total reinsurance recoveries
Written premiums	41,100	35,000		35,600
Long-duration contracts
Premiums
Direct	2,084	3,219		4,753
Assumed	72	85		99
Ceded	(211)	(286)		(398)
Total premiums	$ 1,945	$ 3,018		$ 4,454

[1] Amounts have been restated to reflect the adoption of Targeted Improvements to the Accounting for Long-Duration Contracts in 2023. See Note 2 to the Consolidated Financial Statements for further information.