Goodwill and other intangible assets - Schedule of Finite-Lived Intangible Assets by Major Class (Details) - USD ($) $ in Millions	May 31, 2017	Aug. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 3,927	$ 4,044
Accumulated amortization	1,281	1,439
Total amortizable intangible assets, net	2,646	2,605
Indefinite lived intangible assets	7,562	7,697
Total intangible assets, net	10,208	10,302
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite lived intangible assets	5,507	5,604
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite lived intangible assets	2,055	2,093
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	1,830	1,867
Accumulated amortization	371	275
Purchased prescription files
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	669	932
Accumulated amortization	376	600
Favorable lease interests and non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	536	619
Accumulated amortization	355	388
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	502	532
Accumulated amortization	135	105
Purchasing and payer contracts
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	390	94
Accumulated amortization	$ 44	$ 71