Retirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Retirement Benefits [Abstract]
Service cost	$ 2	$ 2	$ 6	$ 6
Interest cost	3	3	9	10
Expected return on plan assets	(4)	(4)	(12)	(13)
Net actuarial (gain) loss	6	0	6	0
Settlement (gain) loss	0	(9)	0	(15)
Net periodic benefit cost	$ 7	$ (8)	$ 9	$ (12)