Goodwill and other intangible assets - Schedule of Finite-Lived Intangible Assets by Major Class (Details) - USD ($) $ in Millions	May 31, 2020	Aug. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 5,088	$ 5,787
Accumulated amortization	1,787	2,021
Total amortizable intangible assets, net	3,301	3,766
Indefinite-lived intangible assets	6,883	7,110
Total intangible assets, net	10,183	10,876
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	4,997	5,232
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	1,886	1,878
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	4,252	4,290
Accumulated amortization	1,405	1,262
Favorable lease interests and non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	59	654
Accumulated amortization	26	410
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	436	461
Accumulated amortization	248	250
Purchasing and payer contracts
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	341	382
Accumulated amortization	$ 108	$ 99