Goodwill and other intangible assets - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2018	May 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense for intangible assets	$ 146	$ 98	$ 363	$ 287