Investment and derivative contract gains (losses) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Equity securities - Change in unrealized investment gains (losses) during the period on securities held at the end of the period	$ (30,354)	$ (12,902)	$ 33,267	$ (80,496)
Equity securities - Investment gains (losses) on securities sold during the period	605	(165)	1,748	(1,085)
Equity securities - Investment gains (losses), total	(29,749)	(13,067)	35,015	(81,581)
Fixed maturity securities - Gross realized gains	3	6	135	18
Fixed maturity securities - Gross realized losses	(29)	(433)	(106)	(509)
Other	(3)	(6)	2,997	(17)
Investment gains (losses)	(29,778)	(13,500)	38,041	(82,089)
Derivative contract gains (losses)		35		(273)
Investment and derivative contract gains (losses)	$ (29,778)	$ (13,465)	$ 38,041	$ (82,362)