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


	June 30, 2022
	Amortized Cost		Gross Unrealized				Estimated Fair Value
			Gains		Losses

	(In millions)
Corporate debt securities	$	2,372	$	2	$	106	$	2,268
Mortgage-backed securities	759		—		42		717
Asset-backed securities	306		—		13		293
Municipal securities	153		—		7		146
U.S. Treasury notes	96		—		—		96



Other	49		—		2		47
Total	$	3,735	$	2	$	170	$	3,567


	December 31, 2021
	Amortized Cost		Gross Unrealized				Estimated Fair Value
			Gains		Losses

	(In millions)
Corporate debt securities	$	1,836	$	9	$	12	$	1,833
Mortgage-backed securities	616		2		4		614
Asset-backed securities	248		—		1		247
Municipal securities	123		1		1		123
U.S. Treasury notes	353		—		—		353


Other	32		—		—		32
Total	$	3,208	$	12	$	18	$	3,202


	Amortized Cost		Estimated Fair Value

	(In millions)
Due in one year or less	$	340	$	338
Due after one year through five years	2,276		2,175
Due after five years through ten years	377		358
Due after ten years	742		696
Total	$	3,735	$	3,567

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 were insignificant for the six months ended June 30, 2022, and 2021.

We have determined that unrealized losses at June 30, 2022, and December 31, 2021, primarily resulted from fluctuating interest rates, rather than a deterioration of the creditworthiness of the issuers. Therefore, we determined that an allowance for credit losses was not necessary. 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 June 30, 2022:


	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	$	1,971	$	104	921	$	36	$	2	19
Mortgage-backed securities	647		40		273	50		2		26
Asset-backed securities	264		13		134	—		—		—

Municipal securities	100		7		124	—		—		—
Other	27		2		14	—		—		—



Total	$	3,009	$	166	1,466	$	86	$	4	45


	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	$	1,063	$	12	395	$	—	$	—	—
Mortgage-backed securities	408		4		146	—		—		—
Asset-backed securities	166		1		75	—		—		—

Municipal securities	69		1		61	—		—		—



Total	$	1,706	$	18	677	$	—	$	—	—

Pursuant to the regulations governing our state health plan subsidiaries, we maintain statutory deposits and deposits required by government authorities primarily in cash, cash equivalents, 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 “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 $219 million at June 30, 2022, of which $191 million will mature in one year or less, and $28 million will mature in one through five years.