Investment gains/losses (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Equity securities - Unrealized investment gains (losses) on securities held at the end of the period	$ (68,482)	$ 19,393
Equity securities - Investment gains (losses) during the period	(410)	161
Equity securities - Investment gains (losses), total	(68,892)	19,554
Fixed maturity securities - Gross realized gains	16	5
Fixed maturity securities - Gross realized losses	(6)	(10)
Other		3
Investment gains (losses)	$ (68,882)	$ 19,552

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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Amount of gain (loss) included in earnings for investments classified as other.

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