Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Interest and marketable securities income	$ 7	$ 12	$ 18	$ 37
Standard & Poor's, A Rating [Member] | Corporate and asset-backed debt securities
Percentage Of Company's Investments With Credit Quality Rating Less Than Single A And A2			1.00%
Fitch, A Rating [Member] | Corporate and asset-backed debt securities
Percentage Of Company's Investments With Credit Quality Rating Less Than Single A And A2			1.00%
Moody's, A2 Rating [Member] | Corporate and asset-backed debt securities
Percentage Of Company's Investments With Credit Quality Rating Less Than Single A And A2			1.00%