Defined Benefit Pension and Other Postretirement Plans - Components of Net Periodic Pension Expense and Other Postretirement Benefit Costs (Details) - Pension Benefits - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure
Service cost	$ 3	$ 3	$ 9	$ 9
Interest cost	5	6	16	18
Expected return on assets	(10)	(10)	(30)	(29)
Curtailment gain			0	(1)
Amortization of:
Actuarial loss	4	4	11	11
Net cost	$ 2	$ 3	$ 6	$ 8