Summary of major accounting policies - narrative (Details) shares in Millions, $ in Millions	6 Months Ended	12 Months Ended
	Aug. 31, 2021 USD ($) segment	Aug. 31, 2022 USD ($) segment shares	Aug. 31, 2021 USD ($) shares	Aug. 31, 2020 USD ($) shares
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of reportable segments | segment	3	3
Minimum number of days for settlement of credit and debit charges		1 day
Maximum number of days for settlement of credit and debit charges		7 days
Credit and debit card receivables	$ 146	$ 127	$ 146
Other cash flows from operating activities		(146)	(64)	$ 464
Gains on sale-leaseback transactions		619	367	308
Asset impairment impairments		380	203	462
Allowance for doubtful accounts	53	66	53
Inventories	8,159	8,353	8,159
Depreciation and amortization expense		$ 1,400	1,400	1,400
Term of renewal contract		5 years
Advertising expense		$ 862	$ 772	$ 532
Expected performance goal achievement rate		100.00%
Outstanding options to purchase common shares excluded from earnings per share calculations (in shares) | shares		17.1	17.2	19.0
Trade Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	4,500	$ 4,000	$ 4,500
Other Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	1,100	$ 1,100	1,100
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of lease		15 years
Highly effective hedging percentage		80.00%
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of lease		25 years
Highly effective hedging percentage		125.00%
Capitalized system development costs and software
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization of capitalized system development costs and software		$ 307	284	$ 300
Unamortized capitalized software costs	1,100	$ 1,100	1,100
Capitalized system development costs and software | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Estimated useful life		3 years
Capitalized system development costs and software | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Estimated useful life		10 years
Selling, general and administrative expense
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment of definite-lived assets		$ 380	182	$ 401
U.S. Retail Pharmacy | Reportable Segments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Inventories	6,200	6,500	6,200
LIFO reserve	3,300	3,400	3,300
International | Reportable Segments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Inventories	$ 2,000	$ 1,800	$ 2,000