CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 2,977	$ 2,522
Investment securities:
Net unrealized gain (loss)	8	9
Income tax effect	(2)	(3)
Reclassification adjustment for net (gain) loss realized in net income	0	(28)
Income tax effect	0	10
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit (cost)	(7)	0
Income tax effect	1	0
Derivative instruments classified as cash flow hedges:
Net unrealized gain (loss)	38	(1)
Income tax effect	(10)	(5)
Reclassification adjustment for net (gain) loss realized in net income	(25)	11
Income tax effect	5	(2)
Foreign currency translation adjustments	(287)	334
Other comprehensive income (loss), net of tax	(279)	325
Comprehensive income	$ 2,698	$ 2,847