Fair Value Measurements (Marketable Securities) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Estimated Fair Value	$ 4,095	$ 2,947
Available-for-sale marketable securities
Amortized Cost	4,027	2,885
Gross Unrealized Gains	3	6
Gross Unrealized Losses	(2)	(1)
Estimated Fair Value	4,028	2,890
Trading marketable securities
Estimated Fair Value	67	57
Available-for-sale marketable securities
Estimated Fair Value	4,028	2,890
Noncurrent assets-other
Estimated Fair Value	67	57
Corporate and asset-backed debt securities | Available-for-sale marketable securities
Amortized Cost	1,840	1,277
Gross Unrealized Gains	2	4
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	1,841	1,280
Foreign government debt securities | Available-for-sale marketable securities
Amortized Cost	890	846
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(1)
Estimated Fair Value	890	848
United States agency debt securities | Available-for-sale marketable securities
Amortized Cost	519	288
Estimated Fair Value	519	288
United States treasury debt securities | Available-for-sale marketable securities
Amortized Cost	635	343
Estimated Fair Value	635	343
Certificates of deposit | Available-for-sale marketable securities
Amortized Cost	115	114
Estimated Fair Value	115	114
Other | Available-for-sale marketable securities
Amortized Cost	28	17
Estimated Fair Value	$ 28	$ 17