Equity Method Investments (Details) £ in Millions, shares in Millions, $ in Millions				3 Months Ended		9 Months Ended
		Dec. 31, 2014 shares	Aug. 02, 2012 USD ($) shares	May. 31, 2015 USD ($)	May. 31, 2014 USD ($)	May. 31, 2015 USD ($)	May. 31, 2014 USD ($)	Aug. 31, 2014 USD ($)	Aug. 02, 2012 GBP (£)
Schedule of Equity Method Investments [Line Items]
Equity interest in Alliance Boots (in hundredths)				45.00%		45.00%
Shares issued upon exercise of call option (in shares) | shares		144.3
Non-controlling interests				$ 163		$ 163		$ 283
Equity earnings	[1]			$ 7	$ 137	$ 330	$ 467
Alliance Boots [Member]
Schedule of Equity Method Investments [Line Items]
Equity interest in Alliance Boots (in hundredths)		45.00%	45.00%	100.00%		100.00%		45.00%	45.00%
Cash paid to acquire investment			$ 4,025
Shares issued for Investment in Alliance Boots (in shares) | shares			83.4
Remaining ownership subject to call option (in hundredths)			55.00%						55.00%
Cash price to exercise call option | £									£ 3,100
Shares issued upon exercise of call option (in shares) | shares			144.3
Equity method investments investment amount			$ 2,400
Incremental acquisition related amortization				$ 0	11	$ 14	31
Incremental acquisition related amortization, net of tax				11	9	11	25
Non-cash gain resulting from the remeasurement of previously held equity interest						706
Foreign currency translation gains and losses recycled from cumulative other comprehensive income				80		80
Equity earnings					$ 135		$ 465
Other Equity Method Investments [Member]
Schedule of Equity Method Investments [Line Items]
Equity earnings				$ 7		$ 15

[1] Alliance Boots became a consolidated subsidiary and ceased being accounted for under the equity method upon completion of the Second Step Transaction on December 31, 2014. Earnings for the three and nine month periods ended May 31, 2015 reflect incremental acquisition-related amortization expense of zero and $14 million ($11 million net of tax), respectively. Incremental acquisition-related amortization expense for the three and nine month periods ended May 31, 2014 were $11 million ($9 million net of tax) and $31 million ($25 million net of tax), respectively. Earnings in foreign equity method investments are translated at their respective average exchange rates.