Investments of Insurance Subsidiaries - Schedule of Maturities of Investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 76
Due after one year through five years, Amortized Cost	173
Due after five years through ten years, Amortized Cost	120
Due after ten years, Amortized Cost	93
Amortized Cost, Total	462
Amortized Cost	550
Due in one year or less, Fair Value	76
Fair Value	570	628
Due after one year through five years, Fair Value	181
Due after five years through ten years, Fair Value	128
Due after ten years, Fair Value	100
Fair Value, Total	485
Fair Value	567
Auction rate securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	74
Fair Value	68
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14
Fair Value	$ 14