Investments of Insurance Subsidiaries - Schedule of Maturities of Investments (Detail) $ in Millions	Sep. 30, 2015 USD ($)
Amortized Cost and Fair Value Debt Securities [Abstract]
Due in one year or less, Amortized Cost	$ 61
Due after one year through five years, Amortized Cost	172
Due after five years through ten years, Amortized Cost	108
Due after ten years, Amortized Cost	101
Amortized Cost, Total	442
Due in one year or less, Fair Value	61
Due after one year through five years, Fair Value	177
Due after five years through ten years, Fair Value	114
Due after ten years, Fair Value	105
Fair Value, Total	$ 457