Assets and Liabilities Measured at Fair Value - Schedule Related to Auction Rate and Equity Securities Investments of Insurance Subsidiaries at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]
Asset, Beginning Balance	$ 70
Unrealized gains included in other comprehensive income	6
Settlements	(43)
Asset, Ending Balance	$ 33