Segment reporting - results of operations of reportable segments (Details) $ in Millions	3 Months Ended								12 Months Ended
	Aug. 31, 2020 USD ($)	May 31, 2020 USD ($)	Feb. 29, 2020 USD ($)	Nov. 30, 2019 USD ($)	Aug. 31, 2019 USD ($)	May 31, 2019 USD ($)	Feb. 28, 2019 USD ($)	Nov. 30, 2018 USD ($)	Aug. 31, 2020 USD ($) segment	Aug. 31, 2019 USD ($)	Aug. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment									3
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	$ 34,746	$ 34,631	$ 35,820	$ 34,339	$ 33,954	$ 34,591	$ 34,528	$ 33,793	$ 139,537	$ 136,866	$ 131,537
Adjusted operating income									5,211	6,942	7,679
Depreciation and amortization									1,927	2,038	1,770
Capital expenditures									1,374	1,702	1,367
Impairment of goodwill and intangible assets									(2,016)	(73)	0
Transformational cost management									(793)	(477)	0
Acquisition-related amortization									(461)	(493)	(448)
Acquisition-related costs									(316)	(303)	(231)
Adjustments to equity earnings in AmerisourceBergen									(97)	(233)	(175)
LIFO provision									(95)	(136)	(84)
Store damage and inventory losses									(68)	0	0
Store optimization									(53)	(196)	(100)
Certain legal and regulatory accruals and settlements									0	(31)	(284)
Hurricane-related costs									0	0	(83)
Asset recovery									0	0	15
Operating income									1,312	4,998	6,289
Reclassification from selling, general and administrative expenses									(27,045)	(25,242)	(24,694)
Reclassification to other income (expense)									$ 70	$ 233	$ 302
One Third-Party Payer | Revenues
Segment Reporting Information, Operating Income (Loss) [Abstract]
Concentration risk (as a percent)									11.00%
Two Third-Party Payers | Revenues
Segment Reporting Information, Operating Income (Loss) [Abstract]
Concentration risk (as a percent)										22.00%
Three Third-Party Payers | Revenues
Segment Reporting Information, Operating Income (Loss) [Abstract]
Concentration risk (as a percent)											32.00%
Cumulative effect, period of adoption, adjustment
Segment Reporting Information, Operating Income (Loss) [Abstract]
Reclassification from selling, general and administrative expenses											$ 125
Reclassification to other income (expense)											125
Reportable Segments | Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales									$ 107,701	$ 104,532	98,392
Adjusted operating income									4,099	5,255	5,814
Depreciation and amortization									1,385	1,459	1,196
Capital expenditures									1,052	1,323	1,022
Reportable Segments | Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales									10,004	11,462	12,281
Adjusted operating income									130	747	929
Depreciation and amortization									397	429	419
Capital expenditures									239	275	241
Reportable Segments | Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales									23,958	23,053	23,006
Adjusted operating income									980	939	936
Depreciation and amortization									145	150	155
Capital expenditures									83	104	104
Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales									(2,126)	(2,180)	(2,142)
Adjusted operating income									$ 2	$ 1	$ 0
Boots Reporting Unit
Segment Reporting Information, Operating Income (Loss) [Abstract]
Impairment of intangible assets		$ 300
Boots Reporting Unit | Pharmacy licenses
Segment Reporting Information, Operating Income (Loss) [Abstract]
Impairment of intangible assets	$ 73				$ 73