Accumulated other comprehensive loss - Reclassification Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 31, 2025	Jan. 31, 2024	Jan. 31, 2025	Jan. 31, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	$ 94	$ 111	$ 248	$ 283
Net income	276	322	746	841
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial losses	3	3	7	7
Tax benefit	(1)	(1)	(2)	(2)
Net income	$ (2)	$ (2)	$ (5)	$ (5)