Retirement benefit obligations - Level 3 Fair Value Inputs (Details) - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2025	Jul. 31, 2024
Change in assets at fair value:
Beginning balance	$ 1,308	$ 1,270
Impact of exchange rates	34	(1)
Ending balance at fair value	1,182	1,308
Level 3
Change in assets at fair value:
Beginning balance	521	510
Transfers into Level 3	0	11
Transfers out of Level 3	(95)	0
Actual returns	(26)	31
Purchases, sales and settlements, net	(34)	(32)
Impact of exchange rates	12	1
Ending balance at fair value	$ 378	$ 521