CASH, CASH EQUIVALENTS AND INVESTMENTS

Under the terms of the agreements with certain of our workers' compensation and health benefit insurance carriers, we are required to maintain collateral in trust accounts for the benefit of specified insurance carriers and to reimburse the carriers’ claim payments within our deductible layer. We invest a portion of the collateral amounts in marketable securities. We report the current portion of these trust accounts as restricted cash and cash equivalents in WSE-related assets, and the long-term portion as restricted cash, cash equivalents and investments on the consolidated balance sheets.

We require our clients to prefund their payroll and related taxes and other withholding liabilities before payroll is processed or due for payment. This prefund is included in restricted cash, cash equivalents and investments as payroll funds collected, which is designated to pay pending payrolls and other WSE-related liabilities.

Our total cash, cash equivalents and investments are summarized below:



	March 31, 2018								December 31, 2017
(in millions)	Cash and cash equivalents		Available for sale marketable securities		Certificate of deposits		Total		Cash and cash equivalents		Available for sale marketable securities		Certificate of deposits		Total
Cash and cash equivalents	$	330	$	—	$	—	$	330	$	336	$	—	$	—	$	336
Restricted cash, cash equivalents and investments
Insurance carriers security deposits	15		—		—		15		15		—		—		15
Payroll funds collected	523		—		—		523		1,095		—		—		1,095
Collateral for health benefits claims	71		—		—		71		69		—		—		69
Collateral for workers' compensation claims	87		1		—		88		98		1		—		99
Collateral to secure standby letter of credit	—		—		2		2		—		—		2		2
Total restricted cash, cash equivalents and investments	696		1		2		699		1,277		1		2		1,280
Restricted cash, cash equivalents and investments, noncurrent
Collateral for workers' compensation claims	159		23		—		182		125		37		—		162
Total	$	1,185	$	24	$	2	$	1,211	$	1,738	$	38	$	2	$	1,778

The amortized cost, gross unrealized gains, gross unrealized losses, fair values, and related maturities of securities available for sale as of March 31, 2018 and December 31, 2017 are presented below:



(in millions)	Maturity (in years)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
March 31, 2018
U.S. treasuries	1-5 years	$	23	$	—	$	—	$	23
Exchange traded fund	N/A	1		—		—		1
Total		$	24	$	—	$	—	$	24

December 31, 2017
U.S. treasuries	1-5 years	$	37	$	—	$	—	$	37
Exchange traded fund	N/A	1		—		—		1
Total		$	38	$	—	$	—	$	38

There were immaterial realized gains or losses for the three months ended March 31, 2018 and 2017. The fair value of our U.S. Treasury securities in an unrealized loss position represented 89% and 78% of the total fair value of all U.S. Treasury securities as of March 31, 2018 and December 31, 2017, respectively.

Unrealized losses are principally caused by changes in interest rates. In analyzing an issuer's financial condition, we consider whether the securities are issued by the federal government or its agencies, whether downgrades by bond rating agencies have occurred, and industry analysts' reports. As we have the ability to hold these available for sale marketable securities until maturity, or for the foreseeable future, no decline was deemed to be other-than-temporary.