Goodwill and other intangible assets - schedule of finite-lived intangible assets by major class (Details) - USD ($) $ in Millions	Aug. 31, 2019	Aug. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 5,787	$ 5,794
Accumulated amortization	2,021	1,640
Total amortizable intangible assets, net	3,766	4,154
Total indefinite-lived intangible assets	7,110	7,629
Total intangible assets, net	10,876	11,783
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Total indefinite-lived intangible assets	5,232	5,557
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Total indefinite-lived intangible assets	1,878	2,072
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	4,290	4,235
Accumulated amortization	1,262	997
Favorable lease interests and non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	654	680
Accumulated amortization	410	359
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	461	489
Accumulated amortization	250	206
Purchasing and payer contracts
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	382	390
Accumulated amortization	$ 99	$ 78