Defined Benefit Pension and Other Postretirement Plans - Components of Net Periodic Pension Benefit Cost (Income) (Details) - Pension Plan - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure
Service cost	$ 2	$ 2
Interest cost	9	9
Expected return on plan assets	(12)	(11)
Amortization of:
Actuarial loss (gain)	1	0
Net benefit cost (income)	$ 0	$ 0