Fair value measurements - Significant unobservable inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - Equity Securities [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 10,468	$ 12,169	$ 11,480
Gains (losses) included in earnings	$ (805)	$ (40)	$ 689
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	Gain (Loss) on Investments
Acquisitions, dispositions and settlements		$ (1,661)
Ending Balance	$ 9,663	$ 10,468	$ 12,169