Marketable Securities

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

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 AOCI on our accompanying condensed consolidated balance sheets.

Our investments in marketable securities consisted of the following:



	As of September 30, 2018				As of December 31, 2017
(millions)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Corporate debt securities	$	74	$	74	$	68	$	68
U.S. government and agency debt securities	3		3		6		6
Asset-backed debt securities	14		14		11		11
Certificates of deposit	7		7		13		13
Municipal debt securities	1		1		1		1
Total marketable securities	$	99	$	99	$	99	$	99

The realized and unrealized gains and losses for the three and nine months ended September 30, 2018 and 2017 were immaterial. Cost basis for securities sold are determined on a first-in-first-out basis.

Contractual maturities of marketable securities as of September 30, 2018 were as follows:



(millions)	Amortized Cost		Fair Value
Due in 1 year or less	$	61	$	61
Due in 1-5 years	38		38
Total marketable securities	$	99	$	99

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