Accumulated other comprehensive loss - Schedule of Reclassification Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Apr. 30, 2025	Apr. 30, 2024	Apr. 30, 2025	Apr. 30, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	$ 147	$ 138	$ 395	$ 421
Net income	410	443	1,156	1,284
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	5	4	12	11
Tax benefit	(1)	(1)	(3)	(3)
Net income	$ (4)	$ (3)	$ (9)	$ (8)