Fair value measurements - Significant unobservable inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - Equity Securities [Member] - USD ($) $ in Millions |
6 Months Ended | |
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Jun. 30, 2026 |
Jun. 30, 2025 |
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| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | ||
| Beginning Balance | $ 9,529 | $ 9,663 |
| Gains (losses) in earnings | $ 208 | $ (240) |
| Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain (Loss) on Investments | Gain (Loss) on Investments |
| Ending Balance | $ 9,737 | $ 9,423 |
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Indicates line item in statement of income or comprehensive income that includes gain (loss) from asset measured at fair value using unobservable input (level 3). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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