CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 2,329	$ 2,059	$ 7,456	$ 4,559
Investment securities, available-for-sale:
Net unrealized gain	45	22	95	38
Income tax effect	(10)	(9)	(22)	(17)
Reclassification adjustment for net (gain) loss realized in net income	(24)	0	(52)	1
Income tax effect	6	0	16	0
Defined benefit pension and other postretirement plans:
Net unrealized actuarial loss and prior service credit	0	0	(2)	(5)
Income tax effect	0	0	1	2
Reclassification adjustment for net loss realized in net income	4	12	4	33
Income tax effect	(1)	(3)	(1)	(12)
Derivative instruments classified as cash flow hedges:
Net unrealized gain (loss)	114	(20)	72	5
Income tax effect	(19)	5	(22)	9
Reclassification adjustment for net loss realized in net income	10	11	45	31
Income tax effect	0	(5)	(5)	(10)
Foreign currency translation adjustments	(1,112)	1,085	(266)	501
Other comprehensive (loss) income, net of tax	(987)	1,098	(137)	576
Comprehensive income	$ 1,342	$ 3,157	$ 7,319	$ 5,135