Investments of Insurance Subsidiaries - Schedule of Maturities of Investments (Detail) $ in Millions	Jun. 30, 2017 USD ($)
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Amortized Cost	$ 96
Due after one year through five years, Amortized Cost	71
Due after five years through ten years, Amortized Cost	174
Due after ten years, Amortized Cost	43
Amortized Cost, Total	384
Due in one year or less, Fair Value	96
Due after one year through five years, Fair Value	74
Due after five years through ten years, Fair Value	184
Due after ten years, Fair Value	44
Fair Value, Total	$ 398