Exit and disposal activities - Narrative (Details) $ in Millions			3 Months Ended	6 Months Ended	12 Months Ended
	Oct. 12, 2021 USD ($) store	Dec. 20, 2018 USD ($)	Feb. 29, 2024 USD ($) clinic	Feb. 29, 2024 USD ($) store clinic	Aug. 31, 2023 USD ($)	Aug. 31, 2022 USD ($)	Nov. 30, 2023 USD ($)	Feb. 28, 2023 USD ($)	Nov. 30, 2022 USD ($)	Sep. 01, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			$ (15,192)	$ (15,192)	$ (28,322)	$ (29,366)	$ (27,588)	$ (29,439)	$ (24,582)
Asset impairment charges				266
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)	(33,058)	(37,801)	$ (32,573)	$ (33,952)	$ (33,664)
Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			$ 3,400	$ 3,400
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				484
Transformational Cost Management Program | UNITED STATES
Restructuring Cost and Reserve [Line Items]
Number of stores closed | store				625
Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Number of clinics closed | clinic			90
Impairment			$ 179	$ 303
Lease Obligations and Other Real Estate Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			1,300	1,300
Asset Impairments | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			932	932
Employee Severance and Business Transition Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			934	934
Information Technology Transformation and Other Exit Costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			$ 260	$ 260
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