Retirement benefit obligations - Non-Current Asset and Liability in Balance Sheet (Details) - USD ($) $ in Millions	Jul. 31, 2025	Jul. 31, 2024
Retirement Benefits [Abstract]
Non-current asset	$ 26	$ 57

Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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Name:	us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant