Investment gains/losses (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Equity securities - Unrealized investment gains during the period on securities held at the end of the period	$ 30,837	$ 10,489	$ 16,458	$ 39,546
Investment gains/losses on securities sold during the period	1,330	135	(13,901)	464
Equity securities - Investment gains (losses), total	32,167	10,624	2,557	40,010
Fixed maturity securities - Gross realized gains	12	59	53	71
Fixed maturity securities - Gross realized losses	(2)	(2)	(22)	(18)
Other	(552)	11	(556)	16
Investment gains (losses)	$ 31,625	$ 10,692	$ 2,032	$ 40,079

Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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