CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 3,026	$ 3,084	$ 6,152	$ 6,356
Investment securities:
Net unrealized gain (loss)	(1)	5	(2)	5
Income tax effect	0	(1)	0	(1)
Reclassification adjustments	0	(2)	0	(2)
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit (cost)	(2)	3	(3)	2
Income tax effect	1	(1)	2	(1)
Reclassification adjustments	3	2	6	6
Income tax effect	0	0	(1)	(1)
Derivative instruments:
Net unrealized gain (loss)	280	47	(17)	(141)
Income tax effect	(57)	(8)	6	31
Reclassification adjustments	5	(13)	(13)	(15)
Income tax effect	0	3	5	4
Foreign currency translation adjustments	(1,011)	(139)	35	344
Other comprehensive income (loss), net of tax	(782)	(104)	18	231
Comprehensive income	$ 2,244	$ 2,980	$ 6,170	$ 6,587