Marketable Securities (current and non-current) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Marketable securities classification
Current marketable securities	$ 626	$ 756
Non-current marketable securities	828	1,453
Total marketable securities	1,454	2,209
U.S. government agency securities
Marketable securities classification
Current marketable securities	67	103
Non-current marketable securities	41	131
Foreign government agency securities
Marketable securities classification
Current marketable securities	75	30
Non-current marketable securities	20	95
Corporate debt securities
Marketable securities classification
Current marketable securities	241	143
Non-current marketable securities	378	638
Commercial paper
Marketable securities classification
Current marketable securities	0	60
Certificates of deposit/time deposits
Marketable securities classification
Current marketable securities	41	20
Non-current marketable securities	0	20
U.S. treasury securities
Marketable securities classification
Non-current marketable securities	38	49
U.S. municipal securities
Marketable securities classification
Current marketable securities	0	2
Non-current marketable securities	15	0
Asset-backed securities
Marketable securities classification
Current marketable securities	202	398
Non-current marketable securities	336	509
Asset-backed securities Automobile loan related
Marketable securities classification
Current marketable securities	122	287
Non-current marketable securities	160	298
Asset-backed securities Credit card related
Marketable securities classification
Current marketable securities	59	52
Non-current marketable securities	103	128
Asset-backed securities Equipment lease related
Marketable securities classification
Current marketable securities	21	30
Non-current marketable securities	27	37
Asset-backed securities Other asset-backed securities
Marketable securities classification
Current marketable securities	0	29
Non-current marketable securities	46	46
Auction rate securities
Marketable securities classification
Non-current marketable securities	$ 0	$ 11