Retirement benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Nov. 30, 2018	Nov. 30, 2017
Components of net periodic benefit costs [Abstract]
Employer cash contributions to defined benefit pension plans	$ 9
Employee expected additional contribution in current fiscal year	22
Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Total net periodic pension costs (income)	(10)	$ (2)
Walgreen Profit Sharing Retirement Trust
Defined Contribution Plan Disclosure [Line Items]
Profit sharing provision expense	61	57
Alliance Boots Retirement Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Cost recognized in the consolidated condensed statements of earnings	31	30
Selling, general and administrative expenses | Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Service costs	1	2
Other income (expense) | Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Interest costs	49	47
Expected returns on plan assets/other	$ (60)	$ (51)