Investment gains (losses) (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 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	$ 7,593	$ 17,252	$ 1,236	$ 29,711
Equity securities - Investment gains (losses) on securities sold during the period	(370)	6,633	(417)	(3,948)
Equity securities - Investment gains (losses), total	7,223	23,885	819	25,763
Fixed maturity securities - Gross realized gains	8	1	16	14
Fixed maturity securities - Gross realized losses	(8)	(28)	(55)	(40)
Other	(859)	(1)	(851)	(4)
Investment gains (losses)	$ 6,364	$ 23,857	$ (71)	$ 25,733

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
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
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-Publisher FASB
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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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
-Topic 944
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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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