Investment gains/losses (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Equity securities - Change in unrealized investment gains/losses during the year on securities held at the end of the period	$ 54,951	$ 69,581	$ (22,729)
Equity securities - Investment gains/losses during the year on securities sold	(14,036)	1,585	291
Equity securities - Investment gains/losses, total	40,915	71,166	(22,438)
Fixed maturity securities - Gross realized gains	56	87	480
Fixed maturity securities - Gross realized losses	(27)	(25)	(227)
Other	(39)	(105)	30
Investment gains/losses	$ 40,905	$ 71,123	$ (22,155)

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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Amount of realized loss 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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Amount of realized and unrealized gain (loss) on investment.

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