Supplementary financial information - summary of quarterly results (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Aug. 31, 2023	May 31, 2023	Feb. 28, 2023	Nov. 30, 2022	Aug. 31, 2022	May 31, 2022	Feb. 28, 2022	Nov. 30, 2021	Aug. 31, 2023	Aug. 31, 2022	Aug. 31, 2021
Supplementary Financial Information [Abstract]
Sales	$ 35,422	$ 35,415	$ 34,862	$ 33,382	$ 32,449	$ 32,597	$ 33,756	$ 33,901	$ 139,081	$ 132,703	$ 132,509
Gross profit	6,475	6,588	7,055	6,953	6,410	6,572	7,708	7,574	27,072	28,265	28,067
Net (loss) earnings attributable to Walgreens Boots Alliance, Inc.:
Net Income (Loss) Attributable to Parent, Total	$ (180)	$ 118	$ 703	$ (3,721)	$ (415)	$ 289	$ 883	$ 3,580	$ (3,080)	$ 4,337	$ 2,542
Earnings Per Share, Basic [Abstract]
Total (in dollars per share)	$ (0.21)	$ 0.14	$ 0.81	$ (4.31)	$ (0.48)	$ 0.33	$ 1.02	$ 4.13	$ (3.57)	$ 5.02	$ 2.94
Earnings Per Share, Diluted [Abstract]
Total (in dollars per share)	(0.21)	0.14	0.81	(4.31)	(0.48)	0.33	1.02	4.13	(3.57)	5.01	$ 2.93
Cash dividends declared per common share (in dollars per share)	$ 0.4800	$ 0.4800	$ 0.4800	$ 0.4800	$ 0.4800	$ 0.4775	$ 0.4775	$ 0.4775	$ 1.9200	$ 1.9125