Retirement benefit obligations - Schedule of Net Periodic Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Apr. 30, 2025	Apr. 30, 2024	Apr. 30, 2025	Apr. 30, 2024
Retirement Benefits [Abstract]
Interest cost	$ (14)	$ (15)	$ (45)	$ (45)
Expected return on plan assets	16	16	48	46
Amortization of net actuarial losses	(5)	(4)	(12)	(11)
Net periodic cost	$ (3)	$ (3)	$ (9)	$ (10)