Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2012

Investments, Debt and Equity Securities [Abstract]

Investments in marketable securities

Our investments in marketable securities consisted of the following:

	As of September 30, 2012				As of December 31, 2011
(millions)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Corporate debt securities	$	72	$	72	$	174	$	174
U.S. government and agency debt securities	22		22		32		32
Non-U.S. government and agency debt securities	1		1		—		—
Asset-backed debt securities	7		7		18		18
Certificates of deposit	16		16		35		35
Municipal debt securities	12		12		27		27
Total marketable securities	$	130	$	130	$	286	$	286

Contractual maturities of marketable securities

Contractual maturities of marketable securities as of September 30, 2012 were as follows:

(millions)	Amortized Cost		Fair Value
Due in 1 year or less	$	89	$	89
Due in 1-5 years	41		41
Total marketable securities	$	130	$	130