CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net income	$ 20,058	$ 19,743	$ 17,273
Investment securities:
Net unrealized gain (loss)	(23)	120	53
Income tax effect	5	(26)	(11)
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit (cost)	(20)	172	6
Income tax effect	4	(40)	0
Reclassification adjustments	0	9	10
Income tax effect	0	(2)	(2)
Derivative instruments:
Net unrealized gain (loss)	(172)	(38)	(126)
Income tax effect	36	9	24
Reclassification adjustments	55	0	49
Income tax effect	(13)	(7)	(24)
Foreign currency translation adjustments:
Translation adjustments	583	741	975
Income tax effect	101	71	98
Other comprehensive income (loss)	556	1,009	1,052
Comprehensive income	$ 20,614	$ 20,752	$ 18,325