Exit and disposal activities - Narrative (Details) $ in Millions			3 Months Ended	9 Months Ended	12 Months Ended
	Oct. 12, 2021 USD ($) store	Dec. 20, 2018 USD ($)	May 31, 2023 USD ($)	May 31, 2023 USD ($) store	Aug. 31, 2022 USD ($)	Feb. 28, 2023 USD ($)	May 31, 2022 USD ($)	Feb. 28, 2022 USD ($)	Aug. 31, 2021 USD ($)	Sep. 01, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			$ (29,359)	$ (29,359)	$ (29,366)	$ (29,439)	$ (30,382)	$ (30,867)	$ (23,822)
Retained Earnings
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			(33,654)	(33,654)	(37,801)	(33,952)	$ (38,632)	$ (38,757)	$ (35,121)
Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan	$ 3,300		4,100		$ 3,500
Costs incurred			2,700	$ 2,700
Transformational Cost Management Program | United Kingdom
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	350			300
Number of stores closed | store				261
Transformational Cost Management Program | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store				150
Number of stores closed | store				455
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			753	$ 753
Asset Impairments | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			827	827
Employee Severance and Business Transition Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			824	824
Information Technology Transformation and Other Exit Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			247	247
Minimum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan		$ 2,000
Expected cost			3,900	3,900		3,600
Minimum | Transformational Cost Management Program | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	450
Minimum | Exit and Disposal Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost			3,600	3,600		3,300
Maximum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost			4,200	4,200		3,900
Maximum | Transformational Cost Management Program | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	500
Maximum | Exit and Disposal Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost			$ 3,900	$ 3,900		$ 3,600