Exit and disposal activities - narrative (Details) $ in Millions				1 Months Ended	12 Months Ended			30 Months Ended
	Oct. 12, 2021 USD ($) store	Dec. 20, 2018 USD ($)	Oct. 24, 2017 store	Jul. 31, 2021 store	Aug. 31, 2021 USD ($)	Aug. 31, 2020 USD ($)	Aug. 31, 2019 USD ($)	Aug. 31, 2020 USD ($) store	Sep. 01, 2019 USD ($)	Aug. 31, 2018 USD ($)
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings					$ (23,822)	$ (21,136)	$ (24,152)	$ (21,136)		$ (26,689)
Adoption of new accounting standards
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings						6	442	6		88
Retained earnings
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings					(35,121)	(34,210)	(35,815)	(34,210)		(33,551)
Retained earnings | Adoption of new accounting standards
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings						3	442	$ 3		$ 88
Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Costs incurred					1,300
Restructuring costs					335	665	282
Transformational cost management program | United Kingdom
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store				200
Transformational cost management program | United Kingdom | Subsequent event
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	150
Transformational cost management program | United States
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store				250
Transformational cost management program | United States | Subsequent event
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	150
Transformational cost management program | Retained earnings | Adoption of new accounting standards
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings									$ 508
Store optimization program
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store			600
Number of stores closed | store								769
Lease obligations and other real estate costs | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Costs incurred					353
Restructuring costs					108	215	30
Lease obligations and other real estate costs | Store optimization program
Restructuring Cost and Reserve [Line Items]
Restructuring costs						22
Asset impairments | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Costs incurred					252
Restructuring costs					24	72	156
Employee severance and business transition costs | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Costs incurred					513
Restructuring costs					165	270	78
Information technology transformation and other exit costs | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Costs incurred					163
Restructuring costs					38	108	$ 17
Employee severance and other exit costs | Store optimization program
Restructuring Cost and Reserve [Line Items]
Restructuring costs						$ 31
Minimum | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan		$ 2,000
Expected restructuring costs					3,600
Minimum | Transformational cost management program | Subsequent event
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan	$ 3,300
Minimum | Exit and disposal costs | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Expected restructuring costs					3,300
Maximum | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Expected restructuring costs					3,900
Maximum | Exit and disposal costs | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Expected restructuring costs					$ 3,600