Investments And Fair Value Measurements (Short-Term Investments) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Short-term investments	$ 3,408	$ 3,714
Overnight Investments, Time Deposits And Repurchase Agreements [Member]
Schedule of Investments [Line Items]
Short-term investments	306	130
Corporate And Bank Notes [Member]
Schedule of Investments [Line Items]
Short-term investments	2,121	1,808
U.S. Government Agency Mortgages [Member]
Schedule of Investments [Line Items]
Short-term investments	545	502
U.S. Government Agency Notes [Member]
Schedule of Investments [Line Items]
Short-term investments		0
Commingled Funds [Member]
Schedule of Investments [Line Items]
Short-term investments	435	1,274
Other [Member]
Schedule of Investments [Line Items]
Short-term investments	$ 1	$ 0