Investment gains/losses (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Equity securities - Unrealized investment gains (losses) on securities held at the end of the period	$ 10,489	$ 14,294	$ 39,546	$ 12,126
Equity securities - Investment gains (losses) during the period	135	244	464	307
Equity securities - Investment gains (losses), total	10,624	14,538	40,010	12,433
Fixed maturity securities - Gross realized gains	59	44	71	451
Fixed maturity securities - Gross realized losses	(2)	(10)	(18)	(152)
Other	11	(3)	16	18
Investment gains (losses)	$ 10,692	$ 14,569	$ 40,079	$ 12,750

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

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