Retirement benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Nov. 30, 2017	Nov. 30, 2016
Components of net periodic benefit costs [Abstract]
Employer cash contributions to defined benefit pension plans	$ 9
Employee expected additional contribution in current fiscal year	50
Walgreen Profit Sharing Retirement Trust
Defined Contribution Plan Disclosure [Line Items]
Profit sharing provision expense	57	$ 57
Alliance Boots Retirement Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Cost recognized in the consolidated condensed statements of earnings	30	28
Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Service costs	2	2
Interest costs	47	43
Expected returns on plan assets	(51)	(37)
Total net periodic pension costs	$ (2)	$ 8