Retirement benefit obligations - Asset Allocation (Details)	Jul. 31, 2025	Jul. 31, 2024
Defined Benefit Plan Disclosure [Line Items]
Total	100.00%	100.00%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Total	3.00%	2.00%
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	63.00%	63.00%
Cash, cash equivalents and other short-term investments
Defined Benefit Plan Disclosure [Line Items]
Total	1.00%	2.00%
Guaranteed insurance policies
Defined Benefit Plan Disclosure [Line Items]
Total	33.00%	33.00%