Income taxes - deferred tax assets and liabilities (Details) - USD ($) $ in Millions	Aug. 31, 2018	Aug. 31, 2017
Deferred tax assets:
Postretirement benefits	$ 0	$ 134
Compensation and benefits	152	207
Insurance	74	109
Accrued rent	271	174
Outside basis difference	0	55
Allowance for doubtful accounts	27	55
Tax attributes	2,351	555
Stock compensation	44	73
Deferred income	110	220
Other	44	88
Subtotal deferred tax assets	3,073	1,670
Less: valuation allowance	2,226	408
Total deferred tax assets	847	1,262
Deferred tax liabilities:
Accelerated depreciation	603	841
Inventory	301	416
Intangible assets	1,234	1,277
Equity method investment	459	1,002
Total deferred tax liabilities	2,597	3,536
Net deferred tax liabilities	$ 1,750	$ 2,274