Income Taxes - Information that Causes the Income Tax Expense to Differ from the Amount of Income Tax Determined by Applying the Applicable U.S. Federal Statutory Rate of 35% to Pretax Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
U.S. federal income tax at statutory rate	$ 3,809	$ 3,373	$ 2,896
State income taxes, net of federal benefit	216	222	199
Non-U.S. tax effect, net of federal benefit	(588)	(505)	(483)
Remeasurement of deferred tax balances	0	1,007	329
Conclusion of audits	0	(255)	0
State tax apportionment position	(176)	0	0
Other, net	(82)	(90)	(17)
Total income tax provision	$ 3,179	$ 3,752	$ 2,924
U.S. federal income tax at statutory rate, percent	21.00%	21.00%	21.00%
State income taxes, net of federal benefit, percent	1.00%	1.00%	2.00%
Non-U.S. tax effect, net of federal benefit, percent	(3.00%)	(3.00%)	(4.00%)
Remeasurement of deferred tax liability, percent	0.00%	6.00%	2.00%
Conclusion of audits, percent	0.00%	(2.00%)	0.00%
State tax apportionment position, percent	(1.00%)	0.00%	0.00%
Other, net, percent	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Percent, Total	18.00%	23.00%	21.00%