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Fair value measurements - Significant unobservable inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2022
Jun. 30, 2021
Equity Index Put Option Contract Liabilities [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Derivative contract liabilities - Beginning Balance   $ (1,065)
Derivative contract liabilities - Gains included in earnings   710
Derivative contract liabilities - Ending Balance   (355)
Equity Securities [Member]    
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning Balance $ 11,480 8,978
Gains included in earnings 455 1,559
Acquisitions, dispositions and settlements   1,100
Ending Balance $ 11,935 $ 11,637