Summary of significant accounting policies - Narrative (Details)	12 Months Ended
	Jul. 31, 2024 USD ($) extension	Jul. 31, 2023 USD ($)	Jul. 31, 2022 USD ($)
Accounting Policies [Line Items]
Closure charges of underperforming branches	$ 0	$ 125,000,000	$ 0
Rebates receivable	491,000,000	443,000,000
Supplier finance program, obligation, current	$ 46,000,000
Supplier Finance Program, Obligation, Current, Statement of Financial Position [Extensible Enumeration]	Accounts payable
Leases and Related Fixed Assets
Accounting Policies [Line Items]
Closure charges of underperforming branches	$ 0	$ 18,000,000
Minimum
Accounting Policies [Line Items]
Lease term (in years)	3 years
Lease term, extension (in years)	2 years
Maximum
Accounting Policies [Line Items]
Lease term (in years)	10 years
Number of extension periods | extension	4
Lease term, extension (in years)	5 years