Segment reporting (Details) $ in Millions	3 Months Ended
	Nov. 30, 2018 USD ($) segment	Nov. 30, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	3
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	$ 33,793	$ 30,740
Adjusted operating income	1,732	1,806
Acquisition-related amortization	(123)	(85)
Acquisition-related costs	(66)	(51)
Adjustments to equity earnings in AmerisourceBergen	(44)	(189)
LIFO provision	(39)	(54)
Transformational cost management	(30)
Store optimization	(20)
Certain legal and regulatory accruals and settlements	(10)	(25)
Hurricane-related costs		(83)
Operating income	1,400	1,319
Reportable Segments | Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	25,721	22,489
Adjusted operating income	1,379	1,378
Reportable Segments | Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	2,901	3,083
Adjusted operating income	132	205
Reportable Segments | Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	5,708	5,718
Adjusted operating income	220	225
Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	(537)	(550)
Adjusted operating income	1	$ (2)
November 30, 2017 Legal And Regulatory Accruals And Settlements
Segment Reporting Information, Operating Income (Loss) [Abstract]
Adjustments to financial statements to present non-GAAP measures	14
February 28, 2018 Legal And Regulatory Accruals And Settlements
Segment Reporting Information, Operating Income (Loss) [Abstract]
Adjustments to financial statements to present non-GAAP measures	50
May 31, 2018 Legal And Regulatory Accruals And Settlements
Segment Reporting Information, Operating Income (Loss) [Abstract]
Adjustments to financial statements to present non-GAAP measures	$ 5