CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 2,070	$ 1,941
Investment securities, available-for-sale:
Net unrealized (loss) gain	(3)	34
Income tax effect	(1)	(16)
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain and prior service credit	0	56
Income tax effect	0	(21)
Amortization of actuarial loss and prior service credit realized in net income	6	(7)
Income tax effect	(2)	2
Derivative instruments classified as cash flow hedges:
Net unrealized gain	74	16
Income tax effect	(7)	(5)
Reclassification adjustment for net loss (gain) realized in net income	12	(48)
Income tax effect	(2)	14
Foreign currency translation adjustments	(988)	0
Other comprehensive (loss) income, net of tax	(911)	25
Comprehensive income	$ 1,159	$ 1,966