Retirement benefit obligations - Net Periodic Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Oct. 31, 2024	Oct. 31, 2023
Retirement Benefits [Abstract]
Interest cost	$ (16)	$ (15)
Expected return on plan assets	16	15
Amortization of net actuarial losses	(4)	(3)
Net periodic cost	$ (4)	$ (3)