Segment reporting (Details) $ in Millions		3 Months Ended								12 Months Ended
	Dec. 31, 2014 segment	Aug. 31, 2017 USD ($)	May 31, 2017 USD ($)	Feb. 28, 2017 USD ($)	Nov. 30, 2016 USD ($)	Aug. 31, 2016 USD ($)	May 31, 2016 USD ($)	Feb. 29, 2016 USD ($)	Nov. 30, 2015 USD ($)	Aug. 31, 2017 USD ($) segment	Aug. 31, 2016 USD ($)	Aug. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	3									3
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales		$ 30,149	$ 30,118	$ 29,446	$ 28,501	$ 28,636	$ 29,498	$ 30,184	$ 29,033	$ 118,214	$ 117,351	$ 103,444
Adjusted operating income										7,540	7,208	6,157
Depreciation and amortization										1,654	1,718	1,742
Additions to property, plant and equipment										1,351	1,325	1,251
Cost transformation										(835)	(424)	(542)
Acquisition-related costs										(474)	(102)	(87)
Acquisition-related amortization										(332)	(369)	(485)
Adjustments to equity earnings in AmerisourceBergen										(187)	(21)
LIFO provision										(166)	(214)	(285)
Legal settlement											(47)
Asset recovery (impairment)										11	(30)	(110)
Store closures and other optimization costs												(56)
(Loss) on sale of business												(17)
Adjustments to equity earnings in Alliance Boots												93
Operating income										5,557	$ 6,001	$ 4,668
Walgreens Boots Alliance
Segment Reporting Information [Line Items]
Ownership percentage of WBA	55.00%
Alliance Boots
Segment Reporting Information [Line Items]
Equity interest in Alliance Boots	45.00%					45.00%					45.00%	45.00%
Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										87,302	$ 83,802	$ 80,974
Adjusted operating income										5,707	5,357	5,098
Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										11,813	13,256	8,657
Adjusted operating income										909	1,155	616
Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										19,099	20,293	13,813
Adjusted operating income										924	708	450
Operating Segments
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										118,214	117,351	103,444
Operating Segments | Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										87,302	83,802	80,974
Adjusted operating income										5,707	5,357	5,098
Depreciation and amortization										1,090	1,134	1,217
Additions to property, plant and equipment										860	777	951
Operating Segments | Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										11,813	13,256	8,657
Adjusted operating income										909	1,155	616
Depreciation and amortization										414	401	393
Additions to property, plant and equipment										384	444	249
Operating Segments | Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										21,188	22,571	15,327
Adjusted operating income										924	708	450
Depreciation and amortization										150	166	120
Additions to property, plant and equipment										107	104	51
Intersegment Eliminations
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										(2,089)	(2,278)	(1,514)
Adjusted operating income										0	(12)	(7)
Depreciation and amortization										0	17	12
Additions to property, plant and equipment										0	0	0
Intersegment Eliminations | Retail Pharmacy USA
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										0	0	0
Intersegment Eliminations | Retail Pharmacy International
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										0	0	0
Intersegment Eliminations | Pharmaceutical Wholesale
Segment Reporting Information, Operating Income (Loss) [Abstract]
Sales										$ 2,089	$ 2,278	$ 1,514
Top Two Payers | Operating Segments | Retail Pharmacy USA | Revenues
Segment Reporting Information, Operating Income (Loss) [Abstract]
Concentration risk (as a percent)										25.00%	22.00%
Customer One | Operating Segments | Retail Pharmacy International | Revenues
Segment Reporting Information, Operating Income (Loss) [Abstract]
Concentration risk (as a percent)										18.00%	18.00%