Retirement benefit obligations - AOCI (Details) - USD ($) $ in Millions	Jul. 31, 2025	Jul. 31, 2024
Retirement Benefits [Abstract]
Net actuarial loss	$ 667	$ 617
Income tax impact	(159)	(147)
Accumulated other comprehensive loss	$ 508	$ 470

Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant