Fair value measurements - Debt Measured at Fair Value (Details) - USD ($) $ in Millions	Jul. 31, 2024	Jul. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Amount	$ 3,950
Unsecured Senior Notes:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Amount	2,333	$ 2,330
Fair Value	2,263	2,195
Private Placement Notes:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Amount	849	904
Fair Value	$ 837	$ 871