Income tax - Schedule of Reconciliation of Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jul. 31, 2024	Jul. 31, 2025	Jul. 31, 2024	Jul. 31, 2023
Income Tax Disclosure [Abstract]
Provision for income taxes at US and UK statutory rate		$ 509	$ 616	$ 518
Provision for income taxes at US and UK statutory rate (percent)		21.00%	25.00%	21.00%
State and local income tax net of federal income tax benefit		$ 92
State and local income tax net of federal income tax benefit (percent)		3.80%
Non-U.K. tax rate differentials		$ 8	$ (30)	$ 68
Non-UK tax rate differentials (percent)		0.30%	(1.20%)	2.80%
Impact of change in reserves		$ (21)	$ 12	$ 8
Impact of change in reserves (percent)		(0.90%)	0.50%	0.30%
US business tax credits		$ (11)	$ (8)	$ (15)
US business tax credits (percent)		(0.40%)	(0.30%)	(0.60%)
Impact of merger transaction			$ 144	$ 0
Impact of merger transaction (percent)			5.80%	0.00%
Non-taxable income		$ (10)	$ (13)	$ (6)
Non-taxable income (percent)		(0.40%)	(0.50%)	(0.20%)
Other			$ 8	$ 2
Other (percent)			0.30%	0.00%
Provision for income taxes		$ 567	$ 729	$ 575
Income tax expense (percent)		23.40%	29.60%	23.30%
Non-cash deferred tax charges	$ 137
Reversal of tax losses deemed worthless	90
Change in valuation allowance	$ 47