Retirement Plans - Components and Assumptions of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 6	$ 6	$ 5
Interest cost	16	19	18
Expected return on plan assets	$ (13)	$ (12)	$ (12)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other pension expense	Other pension expense	Other pension expense
Net actuarial loss	$ 3	$ 13	$ 19
Settlement loss	4	1	8
Net periodic benefit cost	16	27	$ 38
Pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	6	5
Interest cost	$ 16	$ 19
Pension plan | U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.99%	5.87%	5.51%
Expected return on plan assets	6.75%	6.75%	6.75%
Pension plan | Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.75%	5.60%	4.98%
Expected return on plan assets	5.14%	4.95%	4.53%
Rate of compensation increase	4.38%	4.53%	4.43%