Valuation and Qualifying Accounts (Detail) (Allowance for Doubtful Accounts, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Allowance for Doubtful Accounts
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 3	$ 3	$ 4
Additions charged to costs and expenses	2	2	2
Deductions	(3)	(2)	(3)
Balance at end of period	$ 2	$ 3	$ 3