Exit and disposal activities - Narrative (Details) $ in Millions		3 Months Ended		6 Months Ended
	Oct. 14, 2024 store	Feb. 28, 2025 USD ($)	Feb. 29, 2024 USD ($) clinic	Feb. 28, 2025 USD ($) store clinic	Feb. 29, 2024 USD ($) clinic
Restructuring Cost and Reserve [Line Items]
Costs		$ 68	$ 0	$ 400	$ 0
Impairment			266
Impairment of goodwill, intangibles and long-lived assets				$ 5,660	$ 13,589
Software and Software Development Costs
Restructuring Cost and Reserve [Line Items]
Impairment of goodwill, intangibles and long-lived assets			$ 455
Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Number of clinics closed | clinic			90		160
Footprint Optimization Program
Restructuring Cost and Reserve [Line Items]
Future cash expenditures, percent		0.90		0.90
Costs		$ 68		$ 400
Footprint Optimization Program | Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Costs		42		206
Footprint Optimization Program | Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected cost		300		300
Costs		10		137
Footprint Optimization Program | Employee Severance and Business Transition Costs
Restructuring Cost and Reserve [Line Items]
Expected cost		100		100
Costs		16		$ 57
Footprint Optimization Program And Transformational Cost Management
Restructuring Cost and Reserve [Line Items]
Number of stores closed | store				247
Other Exit Plans
Restructuring Cost and Reserve [Line Items]
Number of clinics closed | clinic				23
Impairment			$ 179		$ 303
Minimum | Footprint Optimization Program
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	900
Expected cost		2,200		$ 2,200
Minimum | Footprint Optimization Program | Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Expected cost		1,800		$ 1,800
Minimum | Footprint Optimization Program And Transformational Cost Management
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store				1,200
Maximum | Footprint Optimization Program
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	1,000
Expected cost		2,400		$ 2,400
Maximum | Footprint Optimization Program | Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Expected cost		$ 2,000		$ 2,000
Maximum | Footprint Optimization Program And Transformational Cost Management
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store				1,300