Exit and disposal activities - restructuring costs (Details) - Store Optimization Program $ in Millions	3 Months Ended
Nov. 30, 2018 USD ($)
Restructuring Reserve Disclosures [Abstract]
Total costs	$ 20
Lease obligations and other real estate costs
Restructuring Reserve Disclosures [Abstract]
Total costs	(7)
Employee severance and other exit costs
Restructuring Reserve Disclosures [Abstract]
Total costs	$ 27

Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Name:	us-gaap_RestructuringCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration