Retirement benefit obligations - Level 3 Fair Value Inputs (Details) - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2024	Jul. 31, 2023
Change in assets at fair value:
Beginning balance	$ 1,270	$ 1,508
Impact of exchange rates	(1)	74
Ending balance at fair value	1,308	1,270
Level 3
Change in assets at fair value:
Beginning balance	510	570
Transfers into Level 3	11	67
Transfers out of Level 3	0	(131)
Actual returns	31	1
Purchases, sales and settlements, net	(32)	(24)
Impact of exchange rates	1	27
Ending balance at fair value	$ 521	$ 510