Investments

Available-for-Sale Investments

We consider all of our investments classified as current assets to be available-for-sale. The following tables summarize our investments as of the dates indicated:



	March 31, 2019
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In millions)
Corporate debt securities	$	949	$	1	$	3	$	947
U.S. Treasury notes	168		—		—		168
GSEs	167		—		1		166
Municipal securities	113		—		1		112
Asset-backed securities	75		—		—		75
Mortgage-backed securities	23		—		—		23
Certificates of deposit	14		—		—		14
Other	3		—		—		3
	$	1,512	$	1	$	5	$	1,508



	December 31, 2018
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In millions)
Corporate debt securities	$	1,131	$	—	$	8	$	1,123
U.S. Treasury notes	181		—		—		181
GSEs	164		—		1		163
Municipal securities	115		—		1		114
Asset-backed securities	83		—		1		82
Certificates of deposit	14		—		—		14
Other	4		—		—		4
Total current investments	$	1,692	$	—	$	11	$	1,681

The contractual maturities of our available-for-sale investments as of March 31, 2019 are summarized below:



	Amortized Cost		Estimated Fair Value
	(In millions)
Due in one year or less	$	927	$	926
Due after one year through five years	550		547
Due after five years through ten years	12		12
Due after ten years	23		23
	$	1,512	$	1,508

Gross realized gains and losses from sales of available-for-sale securities are calculated under the specific identification method and are included in investment income. Gross realized investment gains and losses for the three months ended March 31, 2019 and 2018, were insignificant.

We have determined that unrealized losses at March 31, 2019, and December 31, 2018, are temporary in nature, because the change in market value for these securities has resulted from fluctuating interest rates, rather than a deterioration of the creditworthiness of the issuers. So long as we maintain the intent and ability to hold these securities to maturity, we are unlikely to experience losses. In the event that we dispose of these securities before maturity, we expect that realized losses, if any, will be insignificant.

The following table segregates those available-for-sale investments that have been in a continuous loss position for less than 12 months, and those that have been in a continuous loss position for 12 months or more as of March 31, 2019:



	In a Continuous Loss Position for Less than 12 Months					In a Continuous Loss Position for 12 Months or More
	Estimated Fair Value		Unrealized Losses		Total Number of Positions	Estimated Fair Value		Unrealized Losses		Total Number of Positions
	(Dollars in millions)
Corporate debt securities	$	207	$	1	96	$	403	$	2	280
GSEs	—		—		—	122		1		71
Municipal securities	—		—		—	87		1		91
	$	207	$	1	96	$	612	$	4	442



	In a Continuous Loss Position for Less than 12 Months					In a Continuous Loss Position for 12 Months or More
	Estimated Fair Value		Unrealized Losses		Total Number of Positions	Estimated Fair Value		Unrealized Losses		Total Number of Positions
	(Dollars in millions)
Corporate debt securities	$	509	$	3	285	$	412	$	5	298
GSEs	—		—		—	127		1		76
Municipal securities	—		—		—	87		1		90
Asset-backed securities	—		—		—	68		1		52
	$	509	$	3	285	$	694	$	8	516

Held-to-Maturity Investments

Pursuant to the regulations governing our Health Plans segment subsidiaries, we maintain statutory deposits and deposits required by government authorities primarily in certificates of deposit and U.S. Treasury securities. We also maintain restricted investments as protection against the insolvency of certain capitated providers. The use of these funds is limited as required by regulations in the various states in which we operate, or as needed in the event of insolvency of capitated providers. Therefore, such investments are reported as non-current “Restricted investments” in the accompanying consolidated balance sheets. We have the ability to hold these restricted investments until maturity, and as a result, we would not expect the value of these investments to decline significantly due to a sudden change in market interest rates.

Our held-to-maturity restricted investments are carried at amortized cost, which approximates fair value. Such investments amounted to $100 million at March 31, 2019, and mature in one year or less.