Exit and disposal activities - narrative (Details) $ in Millions		3 Months Ended	12 Months Ended
	Dec. 20, 2018 USD ($)	Feb. 29, 2024 clinic	Aug. 31, 2024 USD ($) clinic store	Aug. 31, 2023 USD ($)	Aug. 31, 2022 USD ($)	Aug. 31, 2021 USD ($)	Sep. 01, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			$ (12,005)	$ (28,322)	$ (29,366)	$ (23,822)
Capitalized system development costs and software
Restructuring Cost and Reserve [Line Items]
Impairment of goodwill, intangibles and long-lived assets			455
Retained earnings
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			(23,348)	(33,058)	$ (37,801)	$ (35,121)
Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan			4,500	$ 3,500
Expected restructuring costs			$ 4,300
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			624
Transformational cost management program | United States
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store			950
Number of stores closed | store			676
Transformational cost management program | Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings							$ 508
Exit and disposal costs | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Expected restructuring costs			$ 4,000
Lease obligations and other real estate costs | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Costs incurred			1,700
Asset impairments | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Costs incurred			1,000
Employee severance and business transition costs | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Costs incurred			1,000
Information technology transformation and other exit costs | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Costs incurred			$ 300
Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Number of clinics closed | clinic		90
Transformational cost management program | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Number of clinics closed | clinic			160
Impairment			$ 303
Minimum | Transformational cost management program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan	$ 2,000