Retirement benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Components of net periodic benefit costs [Abstract]
Employer cash contributions to defined benefit pension plans			$ 11
Employee expected additional contribution in current fiscal year			23
Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Total net periodic pension costs (income)	$ (13)	$ (3)	(23)	$ (5)
Walgreen Profit Sharing Retirement Trust
Defined Contribution Plan Disclosure [Line Items]
Profit sharing provision expense	64	55	125	111
Alliance Boots Retirement Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Cost recognized in the consolidated condensed statements of earnings	33	31	64	61
Selling, general and administrative expenses | Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Service costs	1	1	2	3
Other income (expense) | Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Interest costs	50	49	99	96
Expected returns on plan assets/other	$ (64)	$ (53)	$ (124)	$ (104)