Acquisitions - actual results (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015
Net earnings per common share:
Basic (in dollars per share)	$ 0.76	$ 1.08	$ 0.98	$ 0.97	$ 0.95	$ 1.02	$ 0.86	$ 1.02	$ 3.80	$ 3.85	$ 4.05
Diluted (in dollars per share)	$ 0.76	$ 1.07	$ 0.98	$ 0.97	$ 0.95	$ 1.01	$ 0.85	$ 1.01	$ 3.78	$ 3.82	$ 4.00
Alliance Boots
Business Acquisition [Line Items]
Sales											$ 22,470
Net earnings											$ 853
Net earnings per common share:
Basic (in dollars per share)											$ 0.82
Diluted (in dollars per share)											$ 0.81