Accumulated other comprehensive loss - Reclassification Out of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2024	Jul. 31, 2023	Jul. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	$ 729	$ 575	$ 609
Amounts reclassified from accumulated other comprehensive loss	(1,735)	(1,889)	(2,122)
Reclassification out of Accumulated Other Comprehensive Income | Employee Benefit Trust
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial losses	15	11	10
Tax benefit	(4)	(3)	(2)
Amounts reclassified from accumulated other comprehensive loss	$ 11	$ 8	$ 8