Supplementary financial information - summary of quarterly results (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Aug. 31, 2022	May 31, 2022	Feb. 28, 2022	Nov. 30, 2021	Aug. 31, 2021	May 31, 2021	Feb. 28, 2021	Nov. 30, 2020	Aug. 31, 2022	Aug. 31, 2021	Aug. 31, 2020
Supplementary Financial Information [Abstract]
Sales	$ 32,449	$ 32,597	$ 33,756	$ 33,901	$ 34,262	$ 34,030	$ 32,779	$ 31,438	$ 132,703	$ 132,509	$ 121,982
Gross profit	6,410	6,572	7,708	7,574	7,503	7,153	6,781	6,630	28,265	28,067	26,078
Net earnings attributable to Walgreens Boots Alliance, Inc.:
Continuing operations	(415)	289	883	3,580	358	1,105	922	(391)	4,337	1,994	180
Discontinued operations	0	0	0	0	268	92	104	83	0	548	277
Net earnings attributable to Walgreens Boots Alliance, Inc.	$ (415)	$ 289	$ 883	$ 3,580	$ 627	$ 1,197	$ 1,026	$ (308)	$ 4,337	$ 2,542	$ 456
Basic earnings (loss) per common share:
Continuing operations (in dollars per share)	$ (0.48)	$ 0.33	$ 1.02	$ 4.13	$ 0.41	$ 1.28	$ 1.07	$ (0.45)	$ 5.02	$ 2.31	$ 0.20
Discontinued operations (in dollars per share)	0	0	0	0	0.31	0.11	0.12	0.10	0	0.63	0.31
Total (in dollars per share)	(0.48)	0.33	1.02	4.13	0.72	1.38	1.19	(0.36)	5.02	2.94	0.52
Diluted earnings (loss) per common share:
Continuing operations (in dollars per share)	(0.48)	0.33	1.02	4.13	0.41	1.27	1.06	(0.45)	5.01	2.30	0.20
Discontinued operations (in dollars per share)	0	0	0	0	0.31	0.11	0.12	0.10	0	0.63	0.31
Total (in dollars per share)	(0.48)	0.33	1.02	4.13	0.72	1.38	1.19	(0.36)	5.01	2.93	$ 0.52
Cash dividends declared per common share (in dollars per share)	$ 0.4800	$ 0.4775	$ 0.4775	$ 0.4775	$ 0.4775	$ 0.4675	$ 0.4675	$ 0.4675	$ 1.9125	$ 1.8800