Segment reporting (Details) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2018 USD ($)	May 31, 2017 USD ($)	May 31, 2018 USD ($) segment	May 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	$ 34,334	$ 30,118	$ 98,095	$ 88,065
Adjusted operating income	1,947	1,914	5,919	5,656
Acquisition-related amortization	(131)	(83)	(329)	(247)
Acquisition-related costs	(57)	(29)	(173)	(75)
LIFO provision	(69)	(97)	(166)	(204)
Adjustments to equity earnings in AmerisourceBergen	(60)	(17)	(136)	(95)
Certain legal and regulatory accruals and settlements	(5)		(120)
Hurricane-related costs			(83)
Store optimization	(24)		(24)
Asset recovery			15
Cost transformation		(171)		(592)
Operating income	1,601	1,517	4,903	4,443
Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	25,917	22,528	72,884	65,001
Adjusted operating income	1,492	1,463	4,518	4,304
Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	2,995	2,809	9,395	8,872
Adjusted operating income	198	193	688	648
Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	5,422	4,781	15,816	14,192
Adjusted operating income	257	253	712	703
Reportable Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	34,334	30,118	98,095	88,065
Reportable Segments | Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	25,917	22,528	72,884	65,001
Adjusted operating income	1,492	1,463	4,518	4,304
Reportable Segments | Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	2,995	2,809	9,395	8,872
Adjusted operating income	198	193	688	648
Reportable Segments | Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	5,965	5,296	17,438	15,743
Adjusted operating income	257	253	712	703
Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	(543)	(515)	(1,622)	(1,551)
Adjusted operating income	0	5	1	1
Eliminations | Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	0	0	0	0
Eliminations | Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	0	0	0	0
Eliminations | Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales	$ 543	$ 515	$ 1,622	$ 1,551