Employee Benefit Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Apr. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense (income)	$ (9)	$ (17)	$ (19)	$ (42)
Gain (loss) from actuarial remeasurements			0	8
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement benefit expense (income)	(7)	$ (14)	(14)	$ (28)
Pension plan contributions			9
Expected pension contributions for the remainder of fiscal 2018	$ 9		9
Total expected pension contributions for fiscal 2018			$ 18
Subsequent Event
Defined Benefit Plan Disclosure [Line Items]
Estimated partial withdrawal liability					$ 30