Goodwill and other intangible assets - schedule of finite-lived intangible assets by major class (Details) - USD ($) $ in Millions	Aug. 31, 2018	Aug. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 5,794	$ 3,928
Accumulated amortization	1,640	1,341
Total amortizable intangible assets, net	4,154	2,587
Total indefinite lived intangible assets	7,629	7,569
Total intangible assets, net	11,783	10,156
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Total indefinite lived intangible assets	5,557	5,514
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Total indefinite lived intangible assets	2,072	2,055
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	4,235	2,510
Accumulated amortization	997	780
Favorable lease interests and non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	680	523
Accumulated amortization	359	355
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	489	504
Accumulated amortization	206	155
Total gross amortizable intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	390	391
Accumulated amortization	$ 78	$ 51