Investments of Insurance Subsidiaries - Schedule of Maturities of Investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Amortized Cost and Fair Value Debt Securities [Abstract]
Due in one year or less, Amortized Cost	$ 82
Due after one year through five years, Amortized Cost	229
Due after five years through ten years, Amortized Cost	109
Due after ten years, Amortized Cost	118
Amortized Cost, Total	538
Due in one year or less, Fair Value	82
Due after one year through five years, Fair Value	234
Due after five years through ten years, Fair Value	116
Due after ten years, Fair Value	123
Fair Value, Total	$ 555