Retirement benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Components of net periodic benefit costs [Abstract]
Employer cash contributions to defined benefit pension plans			$ 11
Employee expected additional contribution in current fiscal year			51
Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Service costs	$ 1	$ 0	3	$ 2
Interest costs	49	43	96	86
Expected returns on plan assets	(53)	(36)	(104)	(73)
Curtailments	0	2	0	2
Total net periodic pension costs	(3)	9	(5)	17
Walgreen Profit Sharing Retirement Trust
Defined Contribution Plan Disclosure [Line Items]
Profit sharing provision expense	55	49	111	106
Alliance Boots Retirement Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Cost recognized in the consolidated condensed statements of earnings	$ 31	$ 28	$ 61	$ 56