Exit and disposal activities - Narrative (Details) $ in Millions		3 Months Ended
	Oct. 14, 2024 store	Nov. 30, 2024 USD ($) store clinic	Nov. 30, 2023 USD ($) clinic
Restructuring Cost and Reserve [Line Items]
Costs		$ 333	$ 0
Footprint Optimization Program
Restructuring Cost and Reserve [Line Items]
Future cash expenditures, percent		0.90
Costs		$ 333
Footprint Optimization Program | Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Costs		164
Footprint Optimization Program | Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected cost		300
Costs		127
Footprint Optimization Program | Employee Severance and Business Transition Costs
Restructuring Cost and Reserve [Line Items]
Expected cost		100
Costs		$ 42
Footprint Optimization Program And Transformational Cost Management
Restructuring Cost and Reserve [Line Items]
Number of stores closed | store		83
Other Exit Plans
Restructuring Cost and Reserve [Line Items]
Number of clinics closed | clinic		23	70
Impairment		$ 0	$ 124
Minimum | Footprint Optimization Program
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store	900
Expected cost		2,200
Minimum | Footprint Optimization Program | Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Expected cost		$ 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
Maximum | Footprint Optimization Program | Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Expected cost		$ 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