Investments

Available-for-Sale Investments

We consider all of our investments classified as current assets (including restricted investments) to be available-for-sale. Certain of our senior notes, as further discussed in Note 7, “Debt,” contain a limitation on the use of proceeds which required us to deposit the net proceeds from their issuance into a segregated deposit account, a current asset reported as “Restricted investments” in the accompanying consolidated balance sheets. Such proceeds, while restricted as to their use and held in a segregated deposit account, are available-for-sale based upon our contractual liquidity requirements.

The following tables summarize our investments as of the dates indicated:



	March 31, 2018
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In millions)
Corporate debt securities	$	1,627	$	—	$	9	$	1,618
U.S. treasury notes	330		—		1		329
GSEs	229		—		2		227
Municipal securities	133		—		2		131
Asset backed securities	111		—		1		110
Certificates of deposit	27		—		—		27
Other	2		—		—		2
Subtotal - current investments	2,459		—		15		2,444
Corporate debt securities	66		—		—		66
U.S. treasury notes	11		—		—		11
Subtotal - current restricted investments	77		—		—		77
	$	2,536	$	—	$	15	$	2,521



	December 31, 2017
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In millions)
Corporate debt securities	$	1,591	$	1	$	4	$	1,588
U.S. treasury notes	389		—		1		388
GSEs	255		—		2		253
Municipal securities	142		—		1		141
Asset-backed securities	117		—		—		117
Certificates of deposit	37		—		—		37
Subtotal - current investments	2,531		1		8		2,524
Corporate debt securities	101		—		—		101
U.S. treasury notes	68		—		—		68
Subtotal - current restricted investments	169		—		—		169
	$	2,700	$	1	$	8	$	2,693

The contractual maturities of our available-for-sale investments as of March 31, 2018 are summarized below:



	Amortized Cost		Estimated Fair Value
	(In millions)
Due in one year or less	$	1,576	$	1,573
Due after one year through five years	959		947
Due after five years through ten years	1		1
	$	2,536	$	2,521

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, 2018 and 2017 were insignificant.

We have determined that unrealized losses at March 31, 2018 and December 31, 2017, 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, 2018:



	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	$	1,276	$	7	610	$	93	$	2	71
U.S. Treasury notes	364		1		81	—		—		—
GSEs	179		1		67	95		1		47
Municipal securities	85		1		97	38		1		46
Asset backed securities	97		1		60	—		—		—
	$	2,001	$	11	915	$	226	$	4	164



	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	$	1,297	$	3	561	$	94	$	1	69
U.S. Treasury Notes	470		1		89	—		—		—
GSEs	173		1		69	95		1		47
Municipal securities	—		—		—	38		1		48
	$	1,940	$	5	719	$	227	$	3	164

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.

The contractual maturities of our held-to-maturity restricted investments, which are carried at amortized cost, which approximates fair value, as of March 31, 2018, are summarized below:



	Amortized Cost		Estimated Fair Value
	(In millions)
Due in one year or less	$	117	$	117
Due after one year through five years	3		3
	$	120	$	120