Leases and Store Closures (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	May. 31, 2015 USD ($) Lease	May. 31, 2014 USD ($)	May. 31, 2015 USD ($) Lease	May. 31, 2014 USD ($)	Aug. 31, 2014 USD ($)	Apr. 08, 2015 Store
Lease [Line Items]
Initial term of operating lease, lower range			15 years
Initial term of operating lease, upper range			25 years
Proceeds from sale leaseback transactions			$ 867	$ 144
Financing Obligation [Abstract]
2015	$ 19		19
2016	18		18
2017	18		18
2018	18		18
2019	18		18
Later	1,130		1,130
Total minimum lease payments	1,221		1,221
Capital Lease [Abstract]
2015	68		68
2016	65		65
2017	62		62
2018	59		59
2019	59		59
Later	880		880
Total minimum lease payments	1,193		1,193
Operating Lease [Abstract]
2015	3,110		3,110
2016	3,028		3,028
2017	2,988		2,988
2018	2,755		2,755
2019	2,572		2,572
Later	24,020		24,020
Total minimum lease payments	38,473		38,473
Executory costs and imputed interest	1,500		1,500
Minimum sublease rentals	218		218
Pre-tax charges	0	$ 95	17	95
Lease termination costs		47		47
Asset impairment charges		48		48
Charges related to facilities that were closed or relocated	34	44	60	77
Changes in reserve for facility closings and related lease termination charges [Roll Forward]
Balance - beginning of period			257	123	$ 123
Provision for present value of non-cancellable lease payments on closed facilities			44		171
Assumptions about future sublease income, terminations and changes in interest rates			(2)		(8)
Interest accretion			18		14
Liability assumed through acquisition of Alliance Boots			13		0
Cash payments, net of sublease income			(52)		(43)
Balance - end of period	$ 278		$ 278		$ 257
Number of leases | Lease	72		72
Maximum potential undiscounted future payments	$ 355		$ 355
Rent Expense [Abstract]
Minimum rentals	852	686	2,339	2,020
Contingent rentals	1	1	3	4
Less: Sublease rental income	(15)	(4)	(32)	(16)
Total rental expense	838	$ 683	2,310	$ 2,008
Cost Transformation Program [Member]
Operating Lease [Abstract]
Pre-tax charges	160		160
Asset impairment charges	102		102
Number of stores | Store						200
Severance and other business transition and exit costs	34		34
Real estate costs	$ 24		$ 24