Fair value measurements - Significant unobservable inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Equity Index Put Option Contract Liabilities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative contract liabilities - Beginning Balance		$ (1,065)	$ (968)
Derivative contract liabilities - Gains (losses) included in earnings		$ 966	$ (159)
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Nonoperating Gains (Losses)	Nonoperating Gains (Losses)
Derivative contract liabilities - Acquisitions, dispositions and settlements			$ 62
Derivative contract liabilities - Transfers out of Level 3		$ 99
Derivative contract liabilities - Ending Balance			(1,065)
Equity Securities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 11,480	8,978	10,405
Gains (losses) included in earnings	$ 689	$ 1,902	$ (1,426)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Nonoperating Gains (Losses)	Nonoperating Gains (Losses)	Nonoperating Gains (Losses)
Acquisitions, dispositions and settlements		$ 1,100
Transfers out of Level 3		(500)	$ (1)
Ending Balance	$ 12,169	$ 11,480	$ 8,978