Goodwill and other intangible assets - Schedule of Finite-Lived Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Feb. 29, 2020	Aug. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 5,283	$ 5,787
Accumulated amortization	1,821	2,021
Total amortizable intangible assets, net	3,462	3,766
Indefinite-lived intangible assets	7,466	7,110
Total intangible assets, net	10,929	10,876
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	5,494	5,232
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	1,972	1,878
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	4,397	4,290
Accumulated amortization	1,437	1,262
Favorable lease interests and non-compete agreements1
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	58	654
Accumulated amortization	26	410
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	455	461
Accumulated amortization	255	250
Purchasing and payer contracts
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	373	382
Accumulated amortization	$ 103	$ 99