Income taxes - components of earnings before income tax provision (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015
Income Tax Disclosure [Abstract]
U.S.	$ 1,953	$ 2,577	$ 2,725
Non–U.S.	2,900	2,567	2,586
Earnings before income tax provision	$ 4,853	$ 5,144	$ 5,311