Accumulated other comprehensive income (loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ 30,281	$ 31,300	$ 20,617
Total other comprehensive (loss)	(95)	(2,834)	(356)
Ending Balance	28,274	30,281	31,300
Pension/post-retirement obligations
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(212)	29	15
Other comprehensive income (loss) before reclassification adjustments	(34)	(303)	23
Amounts reclassified from accumulated OCI	109	0	0
Tax benefit (provision)	(2)	62	(9)
Total other comprehensive (loss)	73	(241)	14
Ending Balance	(139)	(212)	29
Unrecognized gain (loss) on available-for-sale investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	2	259	107
Other comprehensive income (loss) before reclassification adjustments	(2)	(148)	247
Amounts reclassified from accumulated OCI	0	(268)	0
Tax benefit (provision)	0	159	(95)
Total other comprehensive (loss)	(2)	(257)	152
Ending Balance	0	2	259
Unrealized gain (loss) on cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(37)	(40)	(27)
Other comprehensive income (loss) before reclassification adjustments	0	0	(14)
Amounts reclassified from accumulated OCI	5	5	(5)
Tax benefit (provision)	(1)	(2)	6
Total other comprehensive (loss)	4	3	(13)
Ending Balance	(33)	(37)	(40)
Share of OCI of equity method investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(1)	0	(113)
Other comprehensive income (loss) before reclassification adjustments	(1)	(1)	(57)
Amounts reclassified from accumulated OCI	0	0	230
Tax benefit (provision)	0	0	(60)
Total other comprehensive (loss)	(1)	(1)	113
Ending Balance	(2)	(1)	0
Cumulative translation adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(2,744)	(462)	154
Other comprehensive income (loss) before reclassification adjustments	(133)	(2,279)	(779)
Amounts reclassified from accumulated OCI	0	(3)	80
Tax benefit (provision)	0	0	83
Total other comprehensive (loss)	(133)	(2,282)	(616)
Ending Balance	(2,877)	(2,744)	(462)
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(2,992)	(214)	136
Other comprehensive income (loss) before reclassification adjustments	(170)	(2,731)	(580)
Amounts reclassified from accumulated OCI	114	(266)	305
Tax benefit (provision)	(3)	219	(75)
Total other comprehensive (loss)	(59)	(2,778)	(350)
Ending Balance	$ (3,051)	$ (2,992)	$ (214)