Fair value measurements - Debt Measured at Fair Value (Details) - USD ($) $ in Millions	Jul. 31, 2025	Jul. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Amount	$ 4,175
Unsecured Senior Notes: | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Amount	3,081	$ 2,333
Fair Value	3,033	2,263
Private Placement Notes: | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Amount	700	849
Fair Value	$ 698	$ 837