Employee Benefit Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense (income)	$ (10)	$ (25)
Gain (loss) from actuarial remeasurements	0	8
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense (income)	(7)	(14)
Pension plan contributions	3
Expected pension contributions for the remainder of fiscal 2018	11
Total expected pension contributions for fiscal 2018	14
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense (income)	$ (3)	$ (11)