Marketable Securities

12 Months Ended

Dec. 31, 2014

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable Securities

Our investments in marketable securities as of December 31, 2014 and 2013 consisted of the following:

	2014				2013
millions	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Corporate debt securities	$	93	$	93	$	87	$	87
U.S. government and agency debt securities	22		22		12		12
Asset-backed debt securities	17		17		20		20
Certificates of deposit	18		18		17		17
Municipal debt securities	4		4		6		6
Total marketable securities	$	154	$	154	$	142	$	142

The realized and unrealized gains and losses as of and for the years ended December 31, 2014, 2013 and 2012 were immaterial.

Contractual maturities of marketable securities as of December 31, 2014 were as follows:

(millions)	Amortized Cost		Fair Value
Due in 1 year or less	$	96	$	96
Due in 1-5 years	58		58
Total marketable securities	$	154	$	154

Actual maturities may differ from the contractual maturities because issuers of the securities may have the right to prepay them.