Investment gains (losses) (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Investments, Debt and Equity Securities [Abstract]
Equity securities - Increase in unrealized investment gains during the period on securities held at the end of the period	$ 20,555	$ 18,643	$ 23,559	$ 45,053
Equity securities - Investment gains (losses) on securities sold during the period	1,365	1,868	(820)	1,221
Equity securities - Investment gains (losses), total	21,920	20,511	22,739	46,274
Fixed maturity securities - Gross realized gains	27	23	43	37
Fixed maturity securities - Gross realized losses	(13)	(17)	(68)	(57)
Other	5	(3)	(846)	(7)
Investment gains (losses)	$ 21,939	$ 20,514	$ 21,868	$ 46,247

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).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Name Accounting Standards Codification
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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of realized and unrealized gain (loss) on investment.

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