Investment gains (losses) (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Investments, Debt and Equity Securities [Abstract]
Equity securities - Change in unrealized investment gains (losses) during the period on securities held at the end of the period	$ 15,644	$ 7,593	$ 12,761	$ 1,236
Equity securities - Investment gains (losses) during the period on securities sold	430	(370)	1,674	(417)
Equity securities - Investment gains (losses), total	16,074	7,223	14,435	819
Fixed maturity securities - Gross realized gains	29	8	76	16
Fixed maturity securities - Gross realized losses	(6)	(8)	(6)	(55)
Other	(20)	(859)	(33)	(851)
Investment gains (losses)	$ 16,077	$ 6,364	$ 14,472	$ (71)

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
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-9

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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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-Name Accounting Standards Codification
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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
-Topic 944
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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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