Supplemental information - Summary of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	Feb. 29, 2020	Aug. 31, 2019	Feb. 28, 2019	Aug. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 792	$ 1,023	$ 792
Restricted cash (included in other current assets)	196	184
Cash, cash equivalents and restricted cash	$ 988	$ 1,207	$ 1,009	$ 975

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant