Exit and disposal activities - Narrative (Details) $ in Millions			3 Months Ended			6 Months Ended	9 Months Ended
	Oct. 12, 2021 USD ($) store	Dec. 20, 2018 USD ($)	Feb. 29, 2024 USD ($) clinic	Nov. 30, 2023 USD ($)	Nov. 30, 2022 USD ($)	Feb. 29, 2024 USD ($) clinic	May 31, 2024 USD ($) store	Aug. 31, 2023 USD ($)	May 31, 2023 USD ($)	Feb. 28, 2023 USD ($)	Aug. 31, 2022 USD ($)	Sep. 01, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			$ (15,192)			$ (15,192)	$ (15,257)	$ (28,322)	$ (29,359)	$ (29,439)	$ (29,366)
Software and Software Development Costs
Restructuring Cost and Reserve [Line Items]
Asset impairment charges			455
Retained Earnings
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			$ (26,448)			$ (26,448)	(26,571)	(33,058)	$ (33,654)	$ (33,952)	$ (37,801)
Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred							$ 3,500
Number of clinics closed | clinic						160
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
Transformational Cost Management Program | United Kingdom
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	650
Number of stores closed | store							581
Transformational Cost Management Program | UNITED STATES
Restructuring Cost and Reserve [Line Items]
Number of stores closed | store							673
Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Number of clinics closed | clinic			90
Impairment						$ 303
Lease Obligations and Other Real Estate Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred							$ 1,300
Asset Impairments | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred							950
Employee Severance and Business Transition Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred							959
Information Technology Transformation and Other Exit Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred							$ 275
Minimum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan	$ 3,300	$ 2,000			$ 3,300
Expected cost								4,100
Minimum | Transformational Cost Management Program | UNITED STATES
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	650
Minimum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan				$ 3,500
Minimum | Exit and Disposal Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost								3,800
Maximum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost								4,400
Maximum | Transformational Cost Management Program | UNITED STATES
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	700
Maximum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan				$ 4,500	$ 3,500
Maximum | Exit and Disposal Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost								$ 4,100