Investments of Insurance Subsidiaries - Schedule of Maturities of Investments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 41
Due after one year through five years, Amortized Cost	176
Due after five years through ten years, Amortized Cost	108
Due after ten years, Amortized Cost	82
Amortized Cost, Total	407
Amortized Cost	452
Due in one year or less, Fair Value	41
Fair Value	465	570
Due after one year through five years, Fair Value	182
Due after five years through ten years, Fair Value	111
Due after ten years, Fair Value	83
Fair Value, Total	417
Fair Value	462
Auction Rate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32
Fair Value	32
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13
Fair Value	$ 13