CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 12,080	$ 10,301	$ 6,699
Investment securities:
Net unrealized gain (loss)	20	94	60
Income tax effect	(5)	(19)	(24)
Reclassification adjustments	1	(215)	1
Income tax effect	0	50	0
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit (cost)	(174)	16	183
Income tax effect	36	(5)	(54)
Reclassification adjustments	9	5	32
Income tax effect	(2)	(1)	(12)
Derivative instruments:
Net unrealized gain (loss)	233	90	(22)
Income tax effect	(25)	(24)	15
Reclassification adjustments	(85)	32	33
Income tax effect	16	(2)	(12)
Foreign currency translation adjustments	(1,228)	(352)	1,136
Other comprehensive income (loss), net of tax	(1,204)	(331)	1,336
Comprehensive income	$ 10,876	$ 9,970	$ 8,035