Income taxes - deferred tax assets and liabilities (Details) - USD ($) $ in Millions	Aug. 31, 2017	Aug. 31, 2016
Deferred tax assets
Postretirement benefits	$ 134	$ 190
Compensation and benefits	207	205
Insurance	109	75
Accrued rent	174	169
Outside basis difference	55	134
Allowance for doubtful accounts	55	65
Tax attributes	555	373
Stock compensation	73	97
Deferred income	220	150
Other	88	195
Subtotal deferred tax assets	1,670	1,653
Less: valuation allowance	408	305
Total deferred tax assets	1,262	1,348
Deferred tax liabilities
Accelerated depreciation	841	1,205
Inventory	416	388
Intangible assets	1,277	1,418
Equity method investment	1,002	978
Deferred income	0	0
Total deferred tax liabilities	3,536	3,989
Net deferred tax liabilities	$ 2,274	$ 2,641