Reinsurance - Supplemental information for loss and benefit reserves, gross and net of ceded reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
As Reported
Liability for unpaid losses and loss adjustment expenses	$ (70,393)	$ (75,167)	$ (79,026)		$ (77,720)
Future policy benefits for life and accident and health insurance contracts	(58,576)	(51,914)		$ (67,364)
Policyholder contract deposits	(161,979)	(155,984)		(148,223)
Unearned premiums	(17,387)	(18,338)
Other policyholder funds	(3,356)	(3,463)		$ (3,796)
Reinsurance assets	62,587	64,810
Net of Reinsurance
Liability for unpaid losses and loss adjustment expenses	(39,994)	(42,955)
Future policy benefits for life and accident and health insurance contracts	(35,005)	(27,836)
Policyholder contract deposits	(158,171)	(152,375)
Reserve for unearned premiums	(13,117)	(13,992)
Other policyholder funds	(2,817)	(2,898)
Reinsurance asset, allowance for credit loss	236	295
Reserve for liability to unpaid losses	110	110
Recoveries of amounts previously written off	0	2
Loss Recoveries
Effects of Reinsurance [Line Items]
Contract claim recoverables	4,879	4,662
Contract Claims Recoverable
Effects of Reinsurance [Line Items]
Contract claim recoverables	$ 296	$ 545