Investment and derivative contract gains/losses (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
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	$ 4,759	$ 30,837	$ 36,163	$ 16,458
Equity securities - Investment gains (losses) on securities sold during the period	75	1,330	889	(13,901)
Equity securities - Investment gains (losses), total	4,834	32,167	37,052	2,557
Fixed maturity securities - Gross realized gains	24	12	59	53
Fixed maturity securities - Gross realized losses	(7)	(2)	(20)	(22)
Other		(552)	144	(556)
Investment gains (losses)	4,851	31,625	37,235	2,032
Derivative contract gains (losses)	70	(43)	780	(640)
Investment and derivative contract gains (losses)	$ 4,921	$ 31,582	$ 38,015	$ 1,392

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 unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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

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The aggregate amount of gains or losses resulting from nonoperating activities (for example, interest and dividend revenue, property, plant and equipment impairment loss, and so forth).

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