Goodwill and other intangible assets - schedule of finite-lived intangible assets by major class (Details) - USD ($) $ in Millions	Aug. 31, 2017	Aug. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	$ 3,928	$ 4,044
Accumulated amortization	1,341	1,439
Total amortizable intangible assets, net	2,587	2,605
Total indefinite lived intangible assets	7,569	7,697
Total intangible assets, net	10,156	10,302
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Total indefinite lived intangible assets	5,514	5,604
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Total indefinite lived intangible assets	2,055	2,093
Customer relationships and loyalty card holders
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	1,851	1,867
Accumulated amortization	409	275
Purchased prescription files
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	659	932
Accumulated amortization	371	600
Favorable lease interests and non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	523	619
Accumulated amortization	355	388
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	504	532
Accumulated amortization	155	105
Total gross amortizable intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross amortizable intangible assets	391	94
Accumulated amortization	$ 51	$ 71