Income Taxes - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Tax Credit Carryforward [Line Items]
US income before taxes	$ 14,776	$ 14,537	$ 13,339
Deferred tax assets, net	$ 1,528	$ 1,641
Effective income tax rate (in percent)	17.00%	17.00%	18.00%
Recognized tax benefit	$ 263	$ 223	$ 142
Income taxes receivable included in prepaid and other current assets	232	832
Income taxes payable included in accrued taxes as part of accrued liabilities	512	577
Accrued income taxes included in other long-term liabilities	309	1,400
Decreased Singapore tax as a result of the tax incentive agreement	$ 453	$ 419	$ 468
Benefit of the tax incentive agreement on diluted net income per share (in dollars per share)	$ 0.23	$ 0.21	$ 0.22
Total unrecognized tax benefits exclusive of interest and penalties	$ 1,672	$ 3,750	$ 3,497	$ 2,683
Unrecognized tax benefits, if recognized, would reduce the effective tax rate in a future period	1,500	1,400	1,600
Interest expense included in interest expense and administrative and other	140	29	34
Accrued interest related to uncertain tax positions in other long term liabilities	160	300
Foreign Country
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards	1,100
Other Assets
Tax Credit Carryforward [Line Items]
Deferred tax assets, net	128	140
Non-current income tax receivable	427	442
Non United States Customers
Tax Credit Carryforward [Line Items]
US income before taxes	$ 6,000	$ 5,100	$ 4,200