Exit and disposal activities - Narrative (Details) $ in Millions			3 Months Ended		9 Months Ended		30 Months Ended
	Dec. 20, 2018 USD ($)	Oct. 24, 2017 store	May 31, 2021 USD ($) segment	May 31, 2020 USD ($)	May 31, 2021 USD ($) store segment	May 31, 2020 USD ($)	Aug. 31, 2020 USD ($) store	Feb. 28, 2021 USD ($)	Feb. 29, 2020 USD ($)	Sep. 01, 2019 USD ($)	Aug. 31, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Number of reportable segments | segment			2		2
Cumulative effect adjustment to decrease retained earnings			$ (22,596)	$ (21,323)	$ (22,596)	$ (21,323)	$ (21,136)	$ (21,625)	$ (24,334)		$ (24,152)
Adoption of new accounting standards
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings							6				442
Retained earnings
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			(34,908)	(34,244)	(34,908)	(34,244)	(34,210)	$ (34,116)	$ (36,351)		(35,815)
Retained earnings | Adoption of new accounting standards
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings							$ 3				$ 442
Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			1,200		1,200
Restructuring charges			44	290	$ 279	455
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 States
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store					250
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			293		$ 293
Restructuring charges			21	173	62	184
Lease obligations and other real estate costs | Store Optimization Program
Restructuring Cost and Reserve [Line Items]
Restructuring charges				3		24
Asset impairments | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			245		245
Restructuring charges			14	29	19	44
Employee severance and business transition costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			517		517
Restructuring charges			(2)	56	172	162
Information technology transformation and other exit costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			153		153
Restructuring charges			11	33	26	65
Employee severance and other exit costs | Store Optimization Program
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 7		$ 25
Minimum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan	$ 2,000
Expected cost			2,100		2,100
Minimum | Exit and disposal costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost			1,800		1,800
Maximum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost			2,300		2,300
Maximum | Exit and disposal costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost			$ 2,000		$ 2,000