Defined Benefit Pension and Other Postretirement Plans - Components of Net Periodic Pension Benefit (Details) - Pension Plan - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure
Service cost	$ 2	$ 2
Interest cost	9	9
Expected return on plan assets	(11)	(11)
Amortization of:
Actuarial gain	0	(1)
Net benefit	$ 0	$ (1)