Segment reporting - results of operations of reportable segments (Details) $ in Millions	3 Months Ended								12 Months Ended
	Aug. 31, 2018 USD ($)	May 31, 2018 USD ($)	Feb. 28, 2018 USD ($)	Nov. 30, 2017 USD ($)	Aug. 31, 2017 USD ($)	May 31, 2017 USD ($)	Feb. 28, 2017 USD ($)	Nov. 30, 2016 USD ($)	Aug. 31, 2018 USD ($) segment	Aug. 31, 2017 USD ($)	Aug. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment									3
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers	$ 33,442	$ 34,334	$ 33,021	$ 30,740	$ 30,149	$ 30,118	$ 29,446	$ 28,501	$ 131,537	$ 118,214	$ 117,351
Adjusted operating income									7,804	7,540	7,208
Depreciation and amortization									1,770	1,654	1,718
Additions to property, plant and equipment									1,367	1,351	1,325
Acquisition-related amortization									(448)	(332)	(369)
Certain legal and regulatory accruals and settlements									(284)		(47)
Acquisition-related costs									(231)	(474)	(102)
Adjustments to equity earnings in AmerisourceBergen									(175)	(187)	(21)
Store optimization									(100)
LIFO provision									(84)	(166)	(214)
Hurricane-related costs									(83)
Cost transformation										(835)	(424)
Asset recovery									15	11	(30)
Operating income									$ 6,414	5,557	6,001
Three Third-Party Payers | Revenues
Segment Reporting Information, Operating Income (Loss) [Abstract]
Concentration risk (as a percent)									32.00%
Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									$ 98,392	87,302	83,802
Adjusted operating income									5,923	5,707	5,357
Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									12,281	11,813	13,256
Adjusted operating income									947	909	1,155
Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									20,864	19,099	20,293
Adjusted operating income									934	924	708
Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									131,537	118,214	117,351
Operating Segments | Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									98,392	87,302	83,802
Adjusted operating income									5,923	5,707	5,357
Depreciation and amortization									1,196	1,090	1,134
Additions to property, plant and equipment									1,022	860	777
Operating Segments | Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									12,281	11,813	13,256
Adjusted operating income									947	909	1,155
Depreciation and amortization									419	414	401
Additions to property, plant and equipment									241	384	444
Operating Segments | Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									23,006	21,188	22,571
Adjusted operating income									934	924	708
Depreciation and amortization									155	150	166
Additions to property, plant and equipment									104	107	104
Intersegment Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									(2,142)	(2,089)	(2,278)
Adjusted operating income									0	0	(12)
Depreciation and amortization									0	0	17
Additions to property, plant and equipment									0	0	0
Intersegment Eliminations | Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									0	0	0
Intersegment Eliminations | Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									0	0	0
Intersegment Eliminations | Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales to external customers									$ 2,142	$ 2,089	$ 2,278