Goodwill and other intangible assets - Schedule of Finite-Lived Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Nov. 30, 2018	Aug. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 5,827	$ 5,794
Accumulated amortization	1,739	1,640
Total amortizable intangible assets, net	4,088	4,154
Indefinite-lived intangible assets	7,496	7,629
Total intangible assets, net	11,584	11,783
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	5,460	5,557
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	2,036	2,072
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	4,291	4,235
Accumulated amortization	1,067	997
Favorable lease interests and non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	668	680
Accumulated amortization	370	359
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	478	489
Accumulated amortization	217	206
Purchasing and payer contracts
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	390	390
Accumulated amortization	$ 85	$ 78