Exit and disposal activities - Restructuring Costs (Details) - Transformational Cost Management Program - USD ($) $ in Millions	3 Months Ended
	Nov. 30, 2022	Nov. 30, 2021
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	$ 130	$ 175
Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	119	123
Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	6	44
Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	4	9
Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	79	89
Lease obligations and other real estate costs | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	79	87
Lease obligations and other real estate costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	0	2
Lease obligations and other real estate costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	0	0
Asset impairments
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	18	40
Asset impairments | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	18	15
Asset impairments | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	0	25
Asset impairments | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	0	0
Employee severance and business transition costs
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	16	37
Employee severance and business transition costs | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	11	20
Employee severance and business transition costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	1	10
Employee severance and business transition costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	4	7
Information technology transformation and other exit costs
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	17	9
Information technology transformation and other exit costs | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	11	1
Information technology transformation and other exit costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	5	7
Information technology transformation and other exit costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	$ 0	$ 1