Restructuring - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Restructuring Cost and Reserve [Line Items]
Cash payment for restructuring	$ 4	$ 6
RM Plan and PC Plan [Member]
Restructuring Cost and Reserve [Line Items]
Severance costs	1	$ 13
Cash payment for restructuring	1
2025 Reorganizations [Member]
Restructuring Cost and Reserve [Line Items]
Severance costs	10
Expected additional restructuring charges	1
Cash payment for restructuring	$ 7