Equity and Noncontrolling Interests Equity and Noncontrolling Interests - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2016
Equity, Class of Treasury Stock [Line Items]
Deferred tax asset from stock options exercised and restricted stock vestings		$ 179
Stock repurchase program, authorized amount		$ 1,000
Treasury Stock, Value, Acquired, Cost Method	$ 49		$ 119		$ 199	$ 119
Stock Repurchase Program, Remaining Authorized Repurchase Amount	1,100				1,100
Post Merger Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount							$ 1,000
Parent
Equity, Class of Treasury Stock [Line Items]
Stockholder's equity, spin-off of Adient	0		(18)	$ (4,020)	0	4,038
Treasury Stock, Value, Acquired, Cost Method	$ 49		$ 119		$ 199	$ 119