Exit and disposal activities - Restructuring Costs (Details) - Transformational Cost Management Program - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2024	May 31, 2023	May 31, 2024	May 31, 2023
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	$ 96	$ 414	$ 368	$ 682
Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	80	104	320	354
Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	14	193	37	204
Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	1	113	5	113
Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	1	4	6	11
Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	38	53	194	151
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	37	35	192	133
Lease obligations and other real estate costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	1	18	2	18
Lease obligations and other real estate costs | Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	0	0	0	0
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	0	0
Asset impairments
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	17	272	66	385
Asset impairments | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	17	12	45	127
Asset impairments | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	0	150	21	149
Asset impairments | Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	0	109	0	109
Asset impairments | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	0	0	0	0
Employee severance and business transition costs
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	26	71	86	102
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	20	50	71	72
Employee severance and business transition costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	4	13	4	15
Employee severance and business transition costs | Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	1	4	5	4
Employee severance and business transition costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	1	4	6	11
Information technology transformation and other exit costs
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	14	19	21	45
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	5	7	11	23
Information technology transformation and other exit costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	9	12	10	22
Information technology transformation and other exit costs | Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	0	0	0	0
Information technology transformation and other exit costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total pre-tax exit and disposal charges	$ 0	$ 0	$ 0	$ 0