CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Net income	$ 19,743	$ 17,273	$ 14,957
Investment securities:
Net unrealized gain (loss)	120	53	(133)
Income tax effect	(26)	(11)	28
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit (cost)	172	6	(168)
Income tax effect	(40)	0	38
Reclassification adjustments	9	10	13
Income tax effect	(2)	(2)	(3)
Derivative instruments:
Net unrealized gain (loss)	(38)	(126)	917
Income tax effect	9	24	(177)
Reclassification adjustments	0	49	(67)
Income tax effect	(7)	(24)	2
Foreign currency translation adjustments:
Translation adjustments	741	975	(3,255)
Income tax effect	71	98	0
Other comprehensive income (loss)	1,009	1,052	(2,805)
Comprehensive income	$ 20,752	$ 18,325	$ 12,152