Employee Benefit Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Apr. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense (income)	$ (10)	$ (16)	$ (29)	$ (58)
Gain (loss) from actuarial remeasurements			0	8
Estimated partial withdrawal liability					$ 30
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense (income)	(7)	$ (13)	(21)	$ (42)
Pension plan contributions			13
Expected pension contributions for the remainder of fiscal 2018	5		5
Total expected pension contributions for fiscal 2018	$ 18		$ 18