Assets and liabilities at fair value - Schedule of Debt Measured at Fair Value (Details) - Level 2 - USD ($) $ in Millions	Oct. 31, 2025	Jul. 31, 2025
Unsecured senior notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Amount	$ 3,827	$ 3,081
Fair Value	3,829	3,033
Private placement notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Amount	300	700
Fair Value	$ 300	$ 698