New accounting pronouncements New accounting pronouncements - Reconciliation of Effect of New Pension and Postretirement Benefits Accounting Guidance (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Nov. 30, 2018	Nov. 30, 2017	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling, general and administrative expenses	$ 6,280	$ 5,910
Operating income	1,400	1,319
Other income (expense)	$ 26	(134)
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling, general and administrative expenses			$ (125)	$ (73)	$ 69
Other income (expense)			$ 125	$ 73	$ (69)
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling, general and administrative expenses		5,907
Operating income		1,322
Other income (expense)		(137)
Adjustments | Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling, general and administrative expenses		3
Operating income		(3)
Other income (expense)		$ 3