CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 2,977	$ 2,605	$ 5,954	$ 5,127
Investment securities:
Net unrealized gain (loss)	7	41	15	50
Income tax effect	(2)	(9)	(4)	(12)
Reclassification adjustment for net (gain) loss realized in net income	0	0	0	(28)
Income tax effect	0	0	0	10
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit (cost)	0	(2)	(7)	(2)
Income tax effect	0	1	1	1
Derivative instruments:
Net unrealized gain (loss)	59	(41)	97	(42)
Income tax effect	(13)	2	(23)	(3)
Reclassification adjustment for net (gain) loss realized in net income	(22)	24	(47)	35
Income tax effect	4	(3)	9	(5)
Foreign currency translation adjustments	(394)	512	(681)	846
Other comprehensive income (loss), net of tax	(361)	525	(640)	850
Comprehensive income	$ 2,616	$ 3,130	$ 5,314	$ 5,977