Defined Benefit Pension and Other Postretirement Plans - Components of Net Periodic Pension Benefit Cost (Income) (Details) - Pension Plan - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Defined Benefit Plan Disclosure
Service cost	$ 2	$ 2	$ 6	$ 7
Interest cost	9	9	27	26
Expected return on plan assets	(11)	(11)	(33)	(34)
Amortization of:
Actuarial loss (gain)	0	(1)	1	(2)
Net benefit cost (income)	$ 0	$ (1)	$ 1	$ (3)