Fair Value Measurements (Marketable Securities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Estimated Fair Value	$ 2,713	$ 2,947
Current assets-marketable securities
Amortized Cost	2,642	2,885
Gross Unrealized Gains	1	6
Gross Unrealized Losses	(2)	(1)
Estimated Fair Value	2,641	2,890
Trading marketable securities
Estimated Fair Value	72	57
Current assets-marketable securities
Estimated Fair Value	2,641	2,890
Noncurrent assets-other
Estimated Fair Value	72	57
Corporate and asset-backed debt securities | Current assets-marketable securities
Amortized Cost	1,177	1,277
Gross Unrealized Gains	1	4
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	1,177	1,280
Foreign government debt securities | Current assets-marketable securities
Amortized Cost	846	846
Gross Unrealized Gains		2
Gross Unrealized Losses	(1)
Estimated Fair Value	845	848
United States agency debt securities | Current assets-marketable securities
Amortized Cost	211	288
Estimated Fair Value	211	288
United States treasury debt securities | Current assets-marketable securities
Amortized Cost	350	343
Estimated Fair Value	350	343
Certificates of deposit | Current assets-marketable securities
Amortized Cost	53	114
Estimated Fair Value	53	114
Other | Current assets-marketable securities
Amortized Cost	5	17
Estimated Fair Value	$ 5	$ 17