Summary of major accounting policies - narrative (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								6 Months Ended	12 Months Ended
	Aug. 31, 2024 USD ($) $ / shares shares	May 31, 2024 $ / shares	Feb. 29, 2024 $ / shares	Nov. 30, 2023 $ / shares	Aug. 31, 2023 USD ($) $ / shares shares	May 31, 2023 $ / shares	Feb. 28, 2023 $ / shares	Nov. 30, 2022 $ / shares	Feb. 28, 2022 USD ($)	Aug. 31, 2024 USD ($) segment $ / shares shares	Aug. 31, 2023 USD ($) $ / shares shares	Aug. 31, 2022 USD ($) shares
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of reportable segments | segment										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	$ 235				$ 122					$ 235	$ 122
Other cash flows from operating activities										(242)	(173)	$ 99
Gain on termination of lease										131
Gain on reclassification of equity method investment to equity security											83
Proceeds from Equity Method Investment, Distribution												46
Equity earnings (loss)										230	286	468
Allowance for doubtful accounts	110				110					110	110
Inventories	$ 8,320				$ 8,257					8,320	8,257
Depreciation and amortization expense										$ 1,500	1,400	1,400
Term of renewal contract	5 years									5 years
Advertising expense										$ 694	$ 775	$ 862
Expected performance goal achievement rate										100.00%
Dividends declared (in dollars per share) | $ / shares	$ 0.2500	$ 0.2500	$ 0.2500	$ 0.4800	$ 0.4800	$ 0.4800	$ 0.4800	$ 0.4800		$ 1.2300	$ 1.9200
Trade Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 4,800				$ 4,300					$ 4,800	$ 4,300
Other Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	1,000				$ 1,100					$ 1,000	$ 1,100
Potentially Dilutive Securities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding options to purchase common shares excluded from earnings per share calculations (in shares) | shares										7.5	3.0
Share-Based Payment Arrangement
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding options to purchase common shares excluded from earnings per share calculations (in shares) | shares										14.1	17.8	17.1
Guoda
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment of equity method investments and investments in equity and debt securities									$ 124	$ 364
VillageMD
Accounts, Notes, Loans and Financing Receivable [Line Items]
Aggregate liquidation preference	$ 4,900									$ 4,900
VillageMD
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-controlling interests, preferred units (in shares) | shares	16.0				16.0					16.0	16.0
Non-controlling interests, common units (in shares) | shares	6.7				6.5					6.7	6.5
Dividend rate	5.50%									5.50%
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of lease	10 years									10 years
Highly effective hedging percentage	80.00%									80.00%
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of lease	25 years									25 years
Highly effective hedging percentage	125.00%									125.00%
Capitalized system development costs and software
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortization of capitalized system development costs and software										$ 414	$ 371	$ 307
Unamortized capitalized software costs	$ 1,400				$ 1,500					1,400	1,500
Impairment of definite-lived assets										455
Selling, general and administrative expense
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment of definite-lived assets										1,700	863	$ 380
U.S. Retail Pharmacy | Reportable Segments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Inventories	6,300				6,200					6,300	6,200
LIFO reserve	3,700				3,600					3,700	3,600
International | Reportable Segments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Inventories	$ 2,000				$ 2,000					$ 2,000	$ 2,000