Marketable Securities

3 Months Ended

Mar. 31, 2012

Marketable Securities [Abstract]

Marketable Securities

6.     Marketable Securities

Marketable securities are classified as available-for-sale securities and reported at fair value, with unrealized gains and losses excluded from earnings and reported in accumulated other comprehensive income (loss), or AOCI, on our condensed consolidated balance sheets. Proceeds received from sales and maturities of marketable securities were $170 million for the three months ended March 31, 2012. Our investments in marketable securities consisted of the following:

	As of March 31, 2012				As of December 31, 2011
(millions)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Corporate debt securities		$          86		$          86		$        174		$        174
U.S. government and agency debt securities		12		12		32		32
Asset-backed debt securities		9		9		18		18
Certificates of deposit		16		16		35		35
Municipal debt securities		15		15		27		27
Total marketable securities		$        138		$        138		$        286		$        286

The realized and unrealized gains and losses for the quarter ended March 31, 2012 and year ended December 31, 2011 were immaterial. Cost basis for securities sold are determined on a first-in-first-out basis.

Contractual maturities of marketable securities as of March 31, 2012 were as follows:

(millions)	Amortized Cost		Fair Value
Due in 1 year or less		$      73		$      73
Due in 1-5 years		65		65
Due in more than 5 years		-		-
Total marketable securities		$    138		$    138

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