Summary of major accounting policies - narrative (Details) shares in Millions, $ in Millions		12 Months Ended
	Sep. 01, 2019 USD ($)	Aug. 31, 2019 USD ($) segment shares	Aug. 31, 2018 USD ($) shares	Aug. 31, 2017 USD ($) shares	Sep. 01, 2018 USD ($)
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		2 days
Maximum number of days for settlement of credit and debit charges		7 days
Credit and debit card receivables		$ 90	$ 127
Restricted cash		184	190
Allowance for doubtful accounts		95	75
Inventories		$ 9,333	9,565
Interval period of renewal options		5 years
Depreciation		$ 1,500	1,400	$ 1,300
Reserve for store closings		993	964
Advertising expense		$ 585	$ 665	$ 571
Outstanding options to purchase common shares excluded from earnings per share calculations (in shares) | shares		14.9	10.1	3.9
Adoption of new accounting standards					$ (88)
Trade Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable		$ 6,000	$ 5,400
Other Accounts Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable		$ 1,200	1,200
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Initial term of operating lease		15 years
Highly effective hedging percentage		80.00%
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Initial term of operating 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		$ 273	254	$ 245
Unamortized capitalized software costs		$ 1,500
Capitalized system development costs and software | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Useful life of capitalized software costs		3 years
Capitalized system development costs and software | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Useful life of capitalized software costs		8 years
Selling, general and administrative expense
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment charges		$ 260	57	234
Accounting standards update 2017-07 | Selling, general and administrative expense
Accounts, Notes, Loans and Financing Receivable [Line Items]
Adoption of new accounting standards			(125)	(73)
Accounting standards update 2017-07 | Other income (expense)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Adoption of new accounting standards			125	$ 73
Retail Pharmacy USA | Operating Segments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Inventories		6,600	6,700
LIFO reserve		3,200	3,000
Retail Pharmacy International and Pharmaceutical Wholesale | Operating Segments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Inventories		$ 2,700	$ 2,800
Retained earnings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Adoption of new accounting standards					(88)
Retained earnings | Accounting standards update 2014-09
Accounts, Notes, Loans and Financing Receivable [Line Items]
Adoption of new accounting standards					$ 98
Forecast | Accounting standards update 2016-02
Accounts, Notes, Loans and Financing Receivable [Line Items]
Adoption of new accounting standards	$ (400)
Operating lease liability	24,000
Operating lease, right-of-use asset	22,000
Impaired long-lived assets	800
De-recognition of deferred gain on sale leaseback transaction	$ (400)