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:


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

	(In millions)
Corporate debt securities	$	2,431	$	—	$	148	$	2,283
Mortgage-backed securities	804		—		61		743
Asset-backed securities	322		—		19		303
Municipal securities	159		—		11		148
U.S. Treasury notes	117		—		1		116



Other	49		—		3		46
Total	$	3,882	$	—	$	243	$	3,639


	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	$	378	$	374
Due after one year through five years	2,330		2,186
Due after five years through ten years	390		364
Due after ten years	784		715
Total	$	3,882	$	3,639

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 were insignificant for the three and nine months ended September 30, 2022, respectively. Gross realized investment gains amounted to $6 million and $7 million for the three and nine months ended September 30, 2021, respectively. Gross realized investment losses were insignificant for the three and nine months ended September 30, 2022, and 2021.

We have determined that unrealized losses at September 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 September 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	$	1,764	$	103	909	$	433	$	45	167
Mortgage-backed securities	555		36		282	188		25		75
Asset-backed securities	242		13		128	56		6		28
Municipal securities	106		7		110	31		4		35
U.S. Treasury notes	116		1		8	—		—		—
Other	32		3		20	—		—		—



Total	$	2,815	$	163	1,457	$	708	$	80	305


	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, U.S. Treasury securities, and corporate debt 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 $242 million at September 30, 2022, of which $201 million will mature in one year or less, $37 million will mature in one through five years, and $4 million will mature after five years.