Investment gains/losses (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investments Debt And Equity Securities [Abstract]
Equity securities - Unrealized investment gains (losses) on securities held at the end of the period	$ 9,827	$ 5,585	$ 29,192	$ (2,146)
Equity securities - Investment gains (losses) during the period	5	357	194	41
Equity securities - Investment gains (losses), total	9,832	5,942	29,386	(2,105)
Fixed maturity securities - Gross realized gains	7	48	12	407
Fixed maturity securities - Gross realized losses	(6)	(4)	(16)	(142)
Other	2	4	5	21
Investment gains (losses)	$ 9,835	$ 5,990	$ 29,387	$ (1,819)

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 realized gain (loss) from sale of 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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