Exit and disposal activities - Restructuring Costs (Details) - Transformational Cost Management Program - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Feb. 28, 2023	Feb. 28, 2022	Feb. 28, 2023	Feb. 28, 2022
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	$ 138	$ 56	$ 267	$ 231
Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	131	43	250	166
Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	4	8	10	51
Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	2	5	6	14
Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	20	5	98	95
Lease obligations and other real estate costs | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	20	5	98	91
Lease obligations and other real estate costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	0	1	0	3
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	95	4	113	44
Asset impairments | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	96	1	115	16
Asset impairments | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	(1)	3	(1)	28
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	15	41	31	79
Employee severance and business transition costs | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	11	36	22	56
Employee severance and business transition costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	1	0	2	9
Employee severance and business transition costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	3	5	7	14
Information technology transformation and other exit costs
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	9	5	25	13
Information technology transformation and other exit costs | Reportable segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	4	1	16	2
Information technology transformation and other exit costs | Reportable segments | International
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	5	4	10	11
Information technology transformation and other exit costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Total exit and disposal charges	$ (1)	$ 0	$ (1)	$ 0