Goodwill and other intangible assets - Schedule of Finite-Lived Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Feb. 28, 2019	Aug. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 5,979	$ 5,794
Accumulated amortization	1,861	1,640
Total amortizable intangible assets, net	4,118	4,154
Indefinite-lived intangible assets	7,814	7,629
Total intangible assets, net	11,932	11,783
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	5,688	5,557
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	2,126	2,072
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	4,421	4,235
Accumulated amortization	1,147	997
Favorable lease interests and non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	669	680
Accumulated amortization	386	359
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	507	489
Accumulated amortization	242	206
Purchasing and payer contracts
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	382	390
Accumulated amortization	$ 86	$ 78