CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 3,126	$ 3,272
Investment securities:
Net unrealized gain (loss)	(1)	0
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit (cost)	(1)	(1)
Income tax effect	1	0
Reclassification adjustments	3	4
Income tax effect	(1)	(1)
Derivative instruments:
Net unrealized gain (loss)	(297)	(188)
Income tax effect	63	39
Reclassification adjustments	(18)	(2)
Income tax effect	5	1
Foreign currency translation adjustments	1,046	483
Other comprehensive income (loss), net of tax	800	335
Comprehensive income	$ 3,926	$ 3,607