Accumulated other comprehensive loss - Reclassification Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Oct. 31, 2024	Oct. 31, 2023
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	$ 154	$ 172
Net income	470	519
Reclassification out of Accumulated Other Comprehensive Income | Employee Benefit Trusts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial losses	4	4
Tax benefit	(1)	(1)
Net income	$ (3)	$ (3)