Exit and disposal activities - Restructuring Costs (Details) - Transformational Cost Management Program - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2023	May 31, 2022	May 31, 2023	May 31, 2022
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	$ 414	$ 173	$ 682	$ 404
Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	104	117	354	283
Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	193	45	204	97
Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	113	0	113	0
Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	4	11	11	25
Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	53	18	151	113
Lease obligations and other real estate costs | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	35	16	133	107
Lease obligations and other real estate costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	18	3	18	6
Lease obligations and other real estate costs | Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total 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 exit and disposal charges	0	0	0	0
Asset impairments
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	272	61	385	105
Asset impairments | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	12	48	127	64
Asset impairments | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	150	14	149	42
Asset impairments | Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	109	0	109	0
Asset impairments | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	0	0	0	0
Employee severance and business transition costs
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	71	86	102	166
Employee severance and business transition costs | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	50	53	72	110
Employee severance and business transition costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	13	22	15	32
Employee severance and business transition costs | Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	4	0	4	0
Employee severance and business transition costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	4	11	11	25
Information technology transformation and other exit costs
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	19	7	45	20
Information technology transformation and other exit costs | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	7	1	23	3
Information technology transformation and other exit costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	12	6	22	18
Information technology transformation and other exit costs | Reportable segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Total 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 exit and disposal charges	$ 0	$ 0	$ 0	$ 0