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	12 Months Ended
	Dec. 31, 2012
Asset balances at December 31, 2011	$ 132
Unrealized gains included in other comprehensive income	3
Settlements	(65)
Asset balances at December 31, 2012	$ 70