Goodwill and other intangible assets - Schedule of Finite-Lived Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Nov. 30, 2019	Aug. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 5,294	$ 5,787
Accumulated amortization	1,753	2,021
Total amortizable intangible assets, net	3,541	3,766
Indefinite-lived intangible assets	7,514	7,110
Total intangible assets, net	11,055	10,876
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	5,529	5,232
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	1,985	1,878
Customer relationships and loyalty card holders1
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	4,391	4,290
Accumulated amortization	1,364	1,262
Favorable lease interests and non-compete agreements2
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	57	654
Accumulated amortization	27	410
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	473	461
Accumulated amortization	264	250
Purchasing and payer contracts
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	373	382
Accumulated amortization	$ 97	$ 99