Investments And Fair Value Measurements (Short-Term Investments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Schedule of Investments [Line Items]
Short-term investments	$ 3,718	$ 4,328
Overnight Investments, Time Deposits And Repurchase Agreements [Member]
Schedule of Investments [Line Items]
Short-term investments	131	844
Corporate And Bank Notes [Member]
Schedule of Investments [Line Items]
Short-term investments	1,808	2,685
U.S. Government Agency Mortgages [Member]
Schedule of Investments [Line Items]
Short-term investments	502	605
U.S. Government Agency Notes [Member]
Schedule of Investments [Line Items]
Short-term investments
Commingled Funds [Member]
Schedule of Investments [Line Items]
Short-term investments	1,274	190
Other [Member]
Schedule of Investments [Line Items]
Short-term investments	$ 3	$ 4