CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 10,866	$ 12,080	$ 10,301
Investment securities:
Net unrealized gain (loss)	1	20	94
Income tax effect	0	(5)	(19)
Reclassification adjustments	(3)	1	(215)
Income tax effect	1	0	50
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit (cost)	(7)	(174)	16
Income tax effect	1	36	(5)
Reclassification adjustments	18	9	5
Income tax effect	(3)	(2)	(1)
Derivative instruments:
Net unrealized gain (loss)	(547)	233	90
Income tax effect	119	(25)	(24)
Reclassification adjustments	(81)	(85)	32
Income tax effect	19	16	(2)
Foreign currency translation adjustments	1,511	(1,228)	(352)
Other comprehensive income (loss), net of tax	1,029	(1,204)	(331)
Comprehensive income	$ 11,895	$ 10,876	$ 9,970