Investments of Insurance Subsidiaries - Schedule of Maturities of Investments (Detail) $ in Millions	Sep. 30, 2016 USD ($)
Amortized Cost and Fair Value Debt Securities [Abstract]
Due in one year or less, Amortized Cost	$ 66
Due after one year through five years, Amortized Cost	123
Due after five years through ten years, Amortized Cost	140
Due after ten years, Amortized Cost	50
Amortized Cost, Total	379
Due in one year or less, Fair Value	66
Due after one year through five years, Fair Value	127
Due after five years through ten years, Fair Value	152
Due after ten years, Fair Value	54
Fair Value, Total	$ 399