Income tax - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jul. 31, 2024	Jul. 31, 2024	Jul. 31, 2023	Jul. 31, 2022
Income Tax Disclosure [Abstract]
Provision for income taxes at UK statutory rate		$ 616	$ 518	$ 515
Provision for income taxes at UK statutory rate (percent)		25.00%	21.00%	19.00%
Non-U.K. tax rate differentials		$ (30)	$ 68	$ 127
Non-UK tax rate differentials (percent)		(1.20%)	2.80%	4.70%
Impact of change in reserves		$ 12	$ 8	$ 8
Impact of change in reserves (percent)		0.50%	0.30%	0.20%
Tax credits		$ (8)	$ (15)	$ (9)
Tax credits (percent)		(0.30%)	(0.60%)	(0.30%)
Impact of merger transaction		$ 144	$ 0	$ 0
Impact of merger transaction (percent)		5.80%	0.00%	0.00%
Non-taxable income		$ (13)	$ (6)	$ (9)
Non-taxable income (percent)		(0.50%)	(0.20%)	(0.30%)
Other		$ 8	$ 2	$ (23)
Other (percent)		0.30%	0.00%	(0.80%)
Provision for income taxes		$ 729	$ 575	$ 609
Income tax expense (percent)		29.60%	23.30%	22.50%
Non-cash deferred tax charges	$ 137	$ (125)	$ 104	$ (41)
Reversal of tax losses deemed worthless	90
Change in valuation allowance	$ 47	$ 47	$ 4	$ 0