Investment gains/losses (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investments Debt And Equity Securities [Abstract]
Equity securities - Unrealized investment gains (losses) on securities held at the end of the period	$ 39,369	$ 9,827	$ (18,377)	$ 29,192
Investment gains (losses) on securities sold during the period	(87)	5	(11,233)	194
Equity securities - Investment gains (losses), total	39,282	9,832	(29,610)	29,386
Fixed maturity securities - Gross realized gains	25	7	41	12
Fixed maturity securities - Gross realized losses	(14)	(6)	(20)	(16)
Other	(4)	2	(4)	5
Investment gains (losses)	$ 39,289	$ 9,835	$ (29,593)	$ 29,387

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

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