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:



	June 30, 2017
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In millions)
Corporate debt securities	$	1,387	$	1	$	2	$	1,386
U.S. treasury notes	263		—		—		263
GSEs	242		—		1		241
Municipal securities	140		—		—		140
Asset-backed securities	128		—		—		128
Certificates of deposit	34		—		—		34
Subtotal - current investments	2,194		1		3		2,192
Corporate debt securities	227		1		—		228
U.S. treasury notes	97		—		—		97
Subtotal - current restricted investments	324		1		—		325
Total	$	2,518	$	2	$	3	$	2,517



	December 31, 2016
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In millions)
Corporate debt securities	$	1,180	$	1	$	2	$	1,179
U.S. treasury notes	84		—		—		84
GSEs	232		—		1		231
Municipal securities	143		—		1		142
Asset-backed securities	69		—		—		69
Certificates of deposit	53		—		—		53
Total - current investments	$	1,761	$	1	$	4	$	1,758

There were no current restricted investments as of December 31, 2016.

The contractual maturities of our available-for-sale investments as of June 30, 2017 are summarized below:



	Amortized Cost		Estimated Fair Value
	(In millions)
Due in one year or less	$	1,301	$	1,301
Due after one year through five years	1,194		1,193
Due after five years through ten years	23		23
Total	$	2,518	$	2,517

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 and six months ended June 30, 2017 and 2016 were insignificant.

We have determined that unrealized losses at June 30, 2017 and December 31, 2016, 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 credit worthiness 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 loss position for 12 months or more as of June 30, 2017:



	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	$	913	$	2	418	$	—	$	—	—
GSEs	247		1		101	—		—		—
Total - current investments	$	1,160	$	3	519	$	—	$	—	—



	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	$	542	$	2	378	$	—	$	—	—
GSEs	198		1		73	—		—		—
Municipal securities	101		1		129	—		—		—
Total - current investments	$	841	$	4	580	$	—	$	—	—

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 regulation 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 sheet. 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 June 30, 2017 are summarized below:



	Amortized Cost		Estimated Fair Value
	(In millions)
Due in one year or less	$	100	$	100
Due after one year through five years	18		17
	$	118	$	117