Investments of Insurance Subsidiaries - Schedule of Maturities of Investments (Detail) $ in Millions	Jun. 30, 2018 USD ($)
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Amortized Cost	$ 24
Due after one year through five years, Amortized Cost	50
Due after five years through ten years, Amortized Cost	218
Due after ten years, Amortized Cost	45
Amortized Cost, Total	337
Due in one year or less, Fair Value	25
Due after one year through five years, Fair Value	50
Due after five years through ten years, Fair Value	221
Due after ten years, Fair Value	45
Fair Value, Total	$ 341

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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