Investments and Fair Value Measurements (Short-Term Investments) (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
Overnight Investments, Time Deposits and Repurchase Agreements [Member]
Schedule of Investments [Line Items]
Short-term investments	177	308
Corporate and Bank Notes [Member]
Schedule of Investments [Line Items]
Short-term investments	3,350	2,121
U.S. Government Agency and Treasury Obligations [Member]
Schedule of Investments [Line Items]
Short-term investments	1,513	545
Commingled Funds [Member]
Schedule of Investments [Line Items]
Short-term investments	3,069	435
Other [Member]
Schedule of Investments [Line Items]
Short-term investments	2	3
AA [Member]
Schedule of Investments [Line Items]
Short-term investments	5,162	3,408
AA [Member] | Overnight Investments, Time Deposits and Repurchase Agreements [Member]
Schedule of Investments [Line Items]
Short-term investments	177	306
AA [Member] | Corporate and Bank Notes [Member]
Schedule of Investments [Line Items]
Short-term investments	3,350	2,121
AA [Member] | U.S. Government Agency and Treasury Obligations [Member]
Schedule of Investments [Line Items]
Short-term investments	1,312	545
AA [Member] | Commingled Funds [Member]
Schedule of Investments [Line Items]
Short-term investments	323	435
AA [Member] | Other [Member]
Schedule of Investments [Line Items]
Short-term investments	$ 0	$ 1