Goodwill and other intangible assets - Schedule of Finite-Lived Intangible Assets by Major Class (Details) - USD ($) $ in Millions	May 31, 2019	Aug. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 5,917	$ 5,794
Accumulated amortization	1,930	1,640
Total amortizable intangible assets, net	3,987	4,154
Indefinite-lived intangible assets	7,338	7,629
Total intangible assets, net	11,325	11,783
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	5,326	5,557
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	2,012	2,072
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	4,329	4,235
Accumulated amortization	1,194	997
Favorable lease interests and non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	661	680
Accumulated amortization	396	359
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	545	489
Accumulated amortization	247	206
Purchasing and payer contracts
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	382	390
Accumulated amortization	$ 93	$ 78