CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES

Components for cash, cash equivalents and marketable securities (in millions):



March 31, 2016	Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Cash	$	3	$	—	$	—		$	3
Cash equivalents	75		—		—			75
Cash and cash equivalents	78		—		—			78
U.S. government and agency securities	410		2		—			412
Foreign government bonds	28		—		—			28
Asset-backed securities	154		1		(1		)	154
Mortgage-backed securities	120		1		—			121
Corporate notes and bonds	749		6		(1		)	754
Municipal securities	17		—		—			17
Marketable securities	1,478		10		(2		)	1,486
Total	$	1,556	$	10	$	(2	)	$	1,564



December 31, 2015	Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Cash	$	4	$	—	$	—		$	4
Cash equivalents	69		—		—			69
Cash and cash equivalents	73		—		—			73
U.S. government and agency securities	254		—		(1		)	253
Foreign government bonds	31		—		—			31
Asset-backed securities	130		—		—			130
Mortgage-backed securities	117		—		(1		)	116
Corporate notes and bonds	711		1		(4		)	708
Municipal securities	17		—		—			17
Marketable securities	1,260		1		(6		)	1,255
Total	$	1,333	$	1	$	(6	)	$	1,328

Unrealized losses from fixed-income securities are primarily attributable to changes in interest rates. Management does not believe any remaining unrealized losses represent other-than-temporary impairments based on our evaluation of available evidence as of March 31, 2016.

Activity for marketable securities (in millions):



	Three Months Ended March 31,
	2016		2015
Proceeds from sales and maturities	$	140	$	259
Gross realized gains	—		1
Gross realized losses	—		(1		)

Maturities for marketable securities (in millions):



March 31, 2016	Cost Basis		Fair Value
Due in one year or less	$	258	$	258
Due after one year through five years	1,218		1,226
Due after five years through 10 years	2		2
Due after 10 years	—		—
Total	$	1,478	$	1,486