Retirement Plans - Schedule of Retirement Plans Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Discontinued Operations
Defined Benefit Plan Disclosure [Line Items]
Total retirement plans expense (income)	$ 7	$ 16	$ 21
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost (benefits earned during the period)	25	49	54
Interest cost	164	99	94
Expected return on plan assets	(247)	(253)	(264)
Net amortization and other	(55)	102	143
Net periodic pension expense (income)	(113)	(3)	27
Defined contribution plans	111	124	114
Total retirement plans expense (income)	(2)	121	141
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost (benefits earned during the period)	20	25	29
Interest cost	50	33	32
Expected return on plan assets	(39)	(56)	(74)
Net amortization and other	18	3	14
Net periodic pension expense (income)	49	5	1
Defined contribution plans	49	52	52
Total retirement plans expense (income)	$ 98	$ 57	$ 53