Investments and Fair Value Measurements (Short-Term Investments by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Short-term investments	$ 8,111	$ 3,412
Due in One Year or Less [Member]
Schedule of Investments [Line Items]
Short-term investments	5,257
Due Between One Year and Three Years [Member]
Schedule of Investments [Line Items]
Short-term investments	2,443
Due After Three Years [Member]
Schedule of Investments [Line Items]
Short-term investments	411
AA [Member]
Schedule of Investments [Line Items]
Short-term investments	5,162	3,408
AA [Member] | Due in One Year or Less [Member]
Schedule of Investments [Line Items]
Short-term investments	2,308
AA [Member] | Due Between One Year and Three Years [Member]
Schedule of Investments [Line Items]
Short-term investments	2,443
AA [Member] | Due After Three Years [Member]
Schedule of Investments [Line Items]
Short-term investments	$ 411