CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 2,522	$ 2,070
Investment securities, available-for-sale:
Net unrealized gain (loss)	9	(3)
Income tax effect	(3)	(1)
Reclassification adjustment for net gain realized in net income	(28)	0
Income tax effect	10	0
Defined benefit pension and other postretirement plans:
Amortization of actuarial loss and prior service credit realized in net income	0	6
Income tax effect	0	(2)
Derivative instruments classified as cash flow hedges:
Net unrealized (loss) gain	(1)	74
Income tax effect	(5)	(7)
Reclassification adjustment for net loss realized in net income	11	12
Income tax effect	(2)	(2)
Foreign currency translation adjustments	334	(988)
Other comprehensive income (loss), net of tax	325	(911)
Comprehensive income	$ 2,847	$ 1,159