Goodwill and other intangible assets - schedule of finite-lived intangible assets by major class (Details) - USD ($) $ in Millions	Aug. 31, 2020	Aug. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Total gross amortizable intangible assets	$ 5,197	$ 5,787
Total accumulated amortization	1,860	2,021
Total amortizable intangible assets, net	3,337	3,766
Total indefinite-lived intangible assets	7,416	7,110
Total intangible assets, net	10,753	10,876
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Total indefinite-lived intangible assets	5,388	5,232
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Total indefinite-lived intangible assets	2,028	1,878
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Total gross amortizable intangible assets	4,389	4,290
Total accumulated amortization	1,511	1,262
Favorable lease interests and non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Total gross amortizable intangible assets	61	654
Total accumulated amortization	26	410
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Total gross amortizable intangible assets	410	461
Total accumulated amortization	228	250
Purchasing and payer contracts
Finite-Lived Intangible Assets [Line Items]
Total gross amortizable intangible assets	337	382
Total accumulated amortization	$ 95	$ 99