Stock-Based Compensation - Stock Options Outstanding and Vested Options (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2015 USD ($)
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Total Options Outstanding, Aggregate Intrinsic Value	$ (4)
Total Options Outstanding, Weighted Average Remaining Contractual Term (in years)	6 years 3 months 18 days
Exercisable Options, Aggregate Intrinsic Value	$ 3
Exercisable Options, Weighted Average Remaining Contractual Term (in years)	5 years 3 months 18 days
Vested or Expected to Vest, Aggregate Intrinsic Value	$ (3)
Vested or Expected to Vest, Weighted Average Remaining Contractual Term (in years)	6 years 3 months 18 days