Retirement benefit obligations - Net Periodic Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 31, 2025	Jan. 31, 2024	Jan. 31, 2025	Jan. 31, 2024
Retirement Benefits [Abstract]
Interest cost	$ (15)	$ (15)	$ (31)	$ (30)
Expected return on plan assets	16	15	32	30
Amortization of net actuarial losses	(3)	(3)	(7)	(7)
Net periodic cost	$ (2)	$ (3)	$ (6)	$ (7)