Exit and disposal activities - Narrative (Details) $ in Millions		3 Months Ended		9 Months Ended
	Oct. 14, 2024 store	May 31, 2025 USD ($) clinic	Feb. 29, 2024 USD ($) clinic	May 31, 2025 USD ($) clinic store	May 31, 2024 USD ($) clinic
Restructuring Cost and Reserve [Line Items]
Impairment			$ 266
Impairment of goodwill, intangibles and long-lived assets				$ 5,776	$ 13,618
Software and Software Development Costs
Restructuring Cost and Reserve [Line Items]
Impairment of goodwill, intangibles and long-lived assets				$ 89	$ 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
Cost incurred to date		$ 473		$ 473
Footprint Optimization Program | Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Cost incurred to date		259		259
Footprint Optimization Program | Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected cost		300		300
Cost incurred to date		135		135
Footprint Optimization Program | Employee Severance and Business Transition Costs
Restructuring Cost and Reserve [Line Items]
Expected cost		100		100
Cost incurred to date		$ 79		$ 79
Footprint Optimization Program And Transformational Cost Management
Restructuring Cost and Reserve [Line Items]
Number of stores closed | store				423
Other Exit Plans
Restructuring Cost and Reserve [Line Items]
Number of clinics closed | clinic		5		28
Impairment				$ 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