Inventories, Net - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Amortization period of pre-production engineering costs	15 years
Amortization expense for pre-production engineering costs	$ 19	$ 11
Weighted-average amortization period remaining for pre-production engineering costs	10 years