Exit and disposal activities - Narrative (Details) $ in Millions			1 Months Ended
	Oct. 12, 2021 USD ($) store	Dec. 20, 2018 USD ($)	Jul. 31, 2021 store	Feb. 28, 2022 USD ($)	Nov. 30, 2021 USD ($)	Aug. 31, 2021 USD ($)	Feb. 28, 2021 USD ($)	Nov. 30, 2020 USD ($)	Aug. 31, 2020 USD ($)	Sep. 01, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings				$ (30,867)	$ (30,579)	$ (23,822)	$ (21,625)	$ (20,563)	$ (21,136)
Adoption of New Accounting Standards
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings									6
Retained Earnings
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings				(38,757)	$ (38,286)	$ (35,121)	$ (34,116)	$ (33,495)	(34,210)
Retained Earnings | Adoption of New Accounting Standards
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings									$ 3
Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred				1,500
Transformational Cost Management Program | United Kingdom
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	150		200
Transformational Cost Management Program | United States
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	150		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
Lease Obligations and Other Real Estate Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred				448
Asset Impairments | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred				296
Employee Severance and Business Transition Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred				592
Information Technology Transformation and Other Exit Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred				175
Minimum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan	$ 3,300	$ 2,000
Expected cost				3,600
Minimum | Exit and Disposal Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost				3,300
Maximum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost				3,900
Maximum | Exit and Disposal Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost				$ 3,600