Debt - short-term borrowings (Details) - USD ($) $ in Millions	Aug. 31, 2018	Aug. 31, 2017
Short-Term Borrowings [Abstract]
Total short-term debt	$ 1,966	$ 251
5.250% unsecured notes due 2019
Short-Term Borrowings [Abstract]
Stated interest rate (as a percent)	5.25%
Other Short Term Debt
Short-Term Borrowings [Abstract]
Total short-term debt	$ 288	251
Commercial Paper
Short-Term Borrowings [Abstract]
Total short-term debt	430	0
Credit facilities
Short-Term Borrowings [Abstract]
Total short-term debt	999	0
Notes Payable | 5.250% unsecured notes due 2019
Short-Term Borrowings [Abstract]
Total short-term debt	$ 249	$ 0