Retirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Retirement Benefits [Abstract]
Service cost	$ 2	$ 2	$ 6	$ 6
Interest cost	3	2	7	8
Expected return on plan assets	(6)	(4)	(14)	(14)
Net actuarial and settlement (gain) loss	(1)	1	(1)	1
Net periodic benefit cost	$ (2)	$ 1	$ (2)	$ 1
Defined Benefit Plan, Type [Extensible Enumeration]			us-gaap:PensionPlansDefinedBenefitMember