Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2012

Fair Value Disclosures [Abstract]

Fair Value Measurements, Recurring and Nonrecurring

The following table summarizes, for assets or liabilities measured at fair value, the respective fair value and the classification by level of input within the fair value hierarchy (in millions):  

			Fair Value Measurement at Reporting Date Using
Description	December 31, 2012		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents:
Money market funds	$	871	$	871	$	—	$	—
Marketable securities:
U.S. government securities	5,165		5,165		—		—
U.S. government agency securities	2,077		2,077		—		—
Total cash equivalents and marketable securities	$	8,113	$	8,113	$	—	$	—
Other current liabilities:
Contingent consideration liability	$	4	$	—	$	—	$	4
Other liabilities:
Derivative financial instrument	$	4	$	—	$	4	$	—

			Fair Value Measurement at Reporting Date Using
Description	December 31, 2011		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3
Cash equivalents:
Money market funds	$	892	$	892	—		—
U.S. government securities	60		60		—		—
U.S. government agency securities	50		50		—		—
Total cash equivalents	1,002		1,002		—		—
Marketable securities:
U.S. government securities	1,415		1,415		—		—
U.S. government agency securities	981		981		—		—
Total cash equivalents and marketable securities	$	3,398	$	3,398	$	—	$	—