Available-For-Sale Investments (Fair Value And Gross Unrealized Losses Of Investments By Length Of Time In Continuous Unrealized Loss Position) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 security		Dec. 31, 2011 security
Total Long-Term Investments [Member]
Schedule Of Available-For-Sale Securities [Line Items]
Number of securities in a loss position	22		22
12 months or greater, Fair value	$ 40		$ 35
12 months or greater, Unrealized losses	(11)	[1]	(23)	[1]
Total, Fair value	40		35
Total, Unrealized losses	(11)		(23)
Asset-Backed Securities [Member]
Schedule Of Available-For-Sale Securities [Line Items]
Number of securities in a loss position	22		22
12 months or greater, Fair value	40		35
12 months or greater, Unrealized losses	(11)	[1]	(23)	[1]
Total, Fair value	40		35
Total, Unrealized losses	$ (11)		$ (23)

[1] Unrealized losses in securities less than 12 months were not significant.