Retirement benefit obligations - Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2025	Jul. 31, 2024	Jul. 31, 2023
Change in net benefit obligations:
Beginning balance	$ 1,251	$ 1,218
Interest cost	62	62	$ 51
Actuarial (gain) loss	(119)	36
Benefits paid	(68)	(63)
Exchange rate adjustment	30	(2)
Ending balance	1,156	1,251	1,218
Change in assets at fair value:
Beginning balance	1,308	1,270
Actual return on plan assets	(123)	68
Company contributions	31	34
Benefits paid	(68)	(63)
Exchange rate adjustment	34	(1)
Ending balance at fair value	1,182	1,308	$ 1,270
Funded status of plans	$ 26	$ 57