Marketable Securities (current and non-current) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Marketable securities classification
Current marketable securities	$ 1,018	$ 626
Non-current marketable securities	13	828
Total marketable securities	1,031	1,454
U.S. government agency securities
Marketable securities classification
Current marketable securities	67	67
Non-current marketable securities	1	41
Foreign government agency securities
Marketable securities classification
Current marketable securities	60	75
Non-current marketable securities	0	20
Corporate debt securities
Marketable securities classification
Current marketable securities	551	241
Non-current marketable securities	0	378
Commercial paper
Marketable securities classification
Current marketable securities	27	0
Certificates of deposit/time deposits
Marketable securities classification
Current marketable securities	24	41
U.S. treasury securities
Marketable securities classification
Non-current marketable securities	0	38
U.S. municipal securities
Marketable securities classification
Current marketable securities	3	0
Non-current marketable securities	12	15
Asset-backed securities
Marketable securities classification
Current marketable securities	286	202
Non-current marketable securities	0	336
Asset-backed securities Automobile loan related
Marketable securities classification
Current marketable securities	167	122
Non-current marketable securities	0	160
Asset-backed securities Credit card related
Marketable securities classification
Current marketable securities	66	59
Non-current marketable securities	0	103
Asset-backed securities Equipment lease related
Marketable securities classification
Current marketable securities	7	21
Non-current marketable securities	0	27
Asset-backed securities Other asset-backed securities
Marketable securities classification
Current marketable securities	46	0
Non-current marketable securities	$ 0	$ 46