Fair value measurements - Significant unobservable inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - Equity Securities [Member] - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 10,468	$ 12,169
Gains (losses) in earnings	$ (699)	$ 190
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
Acquisitions (dispositions)		$ (1,661)
Ending Balance	$ 9,769	$ 10,698

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.

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