CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 3,084	$ 2,977	$ 6,356	$ 5,954
Investment securities:
Net unrealized gain (loss)	5	7	5	15
Income tax effect	(1)	(2)	(1)	(4)
Reclassification adjustments	(2)	0	(2)	0
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit (cost)	3	0	2	(7)
Income tax effect	(1)	0	(1)	1
Reclassification adjustments	2	0	6	0
Income tax effect	0	0	(1)	0
Derivative instruments:
Net unrealized gain (loss)	47	59	(141)	97
Income tax effect	(8)	(13)	31	(23)
Reclassification adjustments	(13)	(22)	(15)	(47)
Income tax effect	3	4	4	9
Foreign currency translation adjustments	(139)	(394)	344	(681)
Other comprehensive income (loss), net of tax	(104)	(361)	231	(640)
Comprehensive income	$ 2,980	$ 2,616	$ 6,587	$ 5,314