Income taxes - narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2024	Aug. 31, 2023	Aug. 31, 2022	Aug. 31, 2021	Aug. 02, 2012
Operating Loss Carryforwards [Line Items]
Effective income tax rate	8.80%	(34.30%)	(0.80%)
Deferred tax assets, tax attributes	$ 7,894	$ 7,784
Income tax credits	189
Deferred tax assets operating loss carryforwards subject to expiration	6,900
Deferred tax assets operating loss carryforwards not subject to expiration	1,000
Valuation allowance	9,642	7,360
Increase in valuation allowance	2,300
Income taxes paid	297	64	$ 387
Unrecognized tax benefits	1,012	1,106	1,110	$ 1,098
Unrecognized tax benefits reported against deferred taxes	394	413
Unrecognized tax benefits reported against tax receivables	75	116
Unrecognized tax benefits would favorably impact the effective tax rate if recognized	618	588	529
Decrease in unrecognized tax benefits is reasonably possible	45
Accrued interest and penalties in income tax provision	182	125
Interest and penalties included in income tax expense	57	29	13
Estimate of possible loss	2,700
Unrecorded deferred tax liability for temporary differences related to foreign subsidiaries		9	104
Tax cuts and jobs act, measurement period adjustment, income tax expense (benefit)			$ (247)
Alliance Boots
Operating Loss Carryforwards [Line Items]
Outstanding equity interest percentage					45.00%
Option to acquire outstanding equity percentage					55.00%
Option to acquire outstanding equity, value					$ 866
Long-term liabilities
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	725	$ 703
U.S. Federal
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	2,500
State
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	1,200
Non-U.S.
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	28,100
U.S. Federal And State
Operating Loss Carryforwards [Line Items]
Increase in valuation allowance	$ 2,200