Cash and Cash Equivalents and Marketable Securities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014 security	Dec. 31, 2013 security	Mar. 31, 2013	Dec. 31, 2012
Cash, Cash Equivalents, and Marketable Securities
Number of positions in a continuous loss position for 12 months or longer	0	0
Cash and cash equivalents:
Cash	$ 1,122	$ 1,044
Money market funds	1,876	2,279
Total cash and cash equivalents	2,998	3,323	2,325	2,384
Marketable securities:
Total marketable securities	9,631	8,126
Total cash, cash equivalents and marketable securities	12,629	11,449
Marketable Securities
Marketable securities:
U.S. government securities	6,759	5,687
U.S. government agency securities	$ 2,872	$ 2,439