Pension and Other Postretirement Benefits (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]
Defined contribution plan, personnel costs	$ 220	$ 212	$ 192
Foreign Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligation	276	302
Funded status	54	68
Accumulated other comprehensive income (loss), defined benefit plan	(65)	(48)
UNITED STATES
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligation	643	670
Funded status	570	531
Accumulated other comprehensive income (loss), defined benefit plan	56	56
Fair Value, Measurements, Recurring | Foreign Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	330	370
Fair Value, Measurements, Recurring | UNITED STATES
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 1,200	$ 1,200