Financial instruments - warrants (Details) - Derivatives not designated as hedges: - Foreign currency forwards - USD ($) $ in Millions	12 Months Ended
Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Selling, general and administrative expense
Warrants [Abstract]
Gains and losses due to changes in fair value of derivative instruments	$ 139	$ 17	$ 11
Other income (expense)
Warrants [Abstract]
Gains and losses due to changes in fair value of derivative instruments	$ (18)	$ 22	$ (48)

Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109977999&loc=d3e76258-113986

Name:	us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration