Restructuring (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		26 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2017	May 31, 2016	May 31, 2017
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	$ 171	$ 73	$ 592	$ 191
Asset impairments
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	114	48	229	73
Real estate costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	15	0	264	52
Severance and other business transition and exit costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	42	25	99	66
Cost Transformation Program
Restructuring Reserve Disclosures [Abstract]
Pre-tax charges incurred during the period					$ 1,600
Restructuring Reserve [Roll Forward]
Beginning Balance			275
Restructuring costs			592
Payments			(131)
Other - non cash			(229)
Currency translation adjustments			0
Ending Balance	507		507		507
Cost Transformation Program | Asset impairments
Restructuring Reserve Disclosures [Abstract]
Pre-tax charges incurred during the period					677
Restructuring Reserve [Roll Forward]
Beginning Balance			0
Restructuring costs			229
Payments			0
Other - non cash			(229)
Currency translation adjustments			0
Ending Balance	0		0		0
Cost Transformation Program | Real estate costs
Restructuring Reserve Disclosures [Abstract]
Pre-tax charges incurred during the period					557
Restructuring Reserve [Roll Forward]
Beginning Balance			248
Restructuring costs			264
Payments			(51)
Other - non cash			0
Currency translation adjustments			0
Ending Balance	461		461		461
Cost Transformation Program | Severance and other business transition and exit costs
Restructuring Reserve Disclosures [Abstract]
Pre-tax charges incurred during the period					324
Restructuring Reserve [Roll Forward]
Beginning Balance			27
Restructuring costs			99
Payments			(80)
Other - non cash			0
Currency translation adjustments			0
Ending Balance	46		46		$ 46
Reportable Segments | Retail Pharmacy USA
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	129	60	517	170
Reportable Segments | Retail Pharmacy USA | Asset impairments
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	96	48	207	73
Reportable Segments | Retail Pharmacy USA | Real estate costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	15	0	264	52
Reportable Segments | Retail Pharmacy USA | Severance and other business transition and exit costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	18	12	46	45
Reportable Segments | Retail Pharmacy International
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	26	6	51	14
Reportable Segments | Retail Pharmacy International | Asset impairments
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	18	0	21	0
Reportable Segments | Retail Pharmacy International | Real estate costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	0	0	0	0
Reportable Segments | Retail Pharmacy International | Severance and other business transition and exit costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	8	6	30	14
Reportable Segments | Pharmaceutical Wholesale
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	16	7	24	7
Reportable Segments | Pharmaceutical Wholesale | Asset impairments
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	0	0	1	0
Reportable Segments | Pharmaceutical Wholesale | Real estate costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	0	0	0	0
Reportable Segments | Pharmaceutical Wholesale | Severance and other business transition and exit costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	$ 16	$ 7	$ 23	$ 7