Valuation And Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Valuation And Qualifying Accounts [Abstract]
Balance at beginning of period	$ 2	$ 3	$ 3
Additions charged to costs and expenses	1	2	2
Deductions	(1)	(3)	(2)
Balance at end of period	$ 2	$ 2	$ 3