Marketable Securities

12 Months Ended

Dec. 31, 2011

Marketable Securities [Abstract]

Marketable Securities

4. Marketable Securities

Our investments in marketable securities as of December 31 consisted of the following:

	2011				2010
(millions)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Corporate debt securities	$	174	$	174	$	123	$	123
U.S. government and agency debt securities		32		32		58		58
Asset-backed debt securities		18		18		19		19
Certificates of deposit		35		35		41		41
Municipal debt securities		27		27		27		27
Non-U.S. government debt securities		—		—		10		10
Total marketable securities	$	286	$	286	$	278	$	278

The realized and unrealized gains and losses as of and for the years ended December 31, 2011 and 2010 were immaterial.

Contractual maturities of marketable securities as of December 31 were as follows:

	2011
(millions)	Amortized Cost		Fair Value
Due in 1 year or less	$	164	$	164
Due in 1-5 years		122		122
Due in more than 5 years		—		—
Total marketable securities	$	286	$	286