Fair Value Measurements (Marketable Securities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Document Fiscal Year Focus	2014
Estimated Fair Value	$ 2,740		$ 2,713
Available-for-sale marketable securities
Amortized Cost	2,663		2,642
Gross Unrealized Gains	4	1
Gross Unrealized Losses	(1)	(2)
Estimated Fair Value	2,666		2,641
Trading marketable securities
Estimated Fair Value	74		72
Available-for-sale marketable securities
Estimated Fair Value	2,666		2,641
Noncurrent assets-other
Estimated Fair Value	74		72
Corporate and asset-backed debt securities | Available-for-sale marketable securities
Amortized Cost	1,171		1,177
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	1,172		1,177
Foreign government debt securities | Available-for-sale marketable securities
Amortized Cost	826		846
Gross Unrealized Gains	2
Gross Unrealized Losses		(1)
Estimated Fair Value	828		845
United States agency debt securities | Available-for-sale marketable securities
Amortized Cost	124		211
Estimated Fair Value	124		211
United States treasury debt securities | Available-for-sale marketable securities
Amortized Cost	487		350
Estimated Fair Value	487		350
Certificates of deposit | Available-for-sale marketable securities
Amortized Cost	51		53
Estimated Fair Value	51		53
Other | Available-for-sale marketable securities
Amortized Cost	4		5
Estimated Fair Value	$ 4		$ 5