Fair Value of Financial Investments and Liabilities - Changes in Level 3 Financial Assets Measured at Fair Value on Recurring Basis (Detail) (Auction Rate Securities [Member], USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value at beginning of period	$ 22	$ 22
Total losses included in earnings
Unrealized (losses)
Purchases
Settlements
Transfer from Level 3 to Level 2
Fair value at period end	$ 22	$ 22