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, 2024
	Amortized Cost		Gross Unrealized				Estimated Fair Value
			Gains		Losses

	(In millions)
Corporate debt securities	$	2,852	$	6	$	57	$	2,801
Mortgage-backed securities	967		2		45		924
Asset-backed securities	392		1		10		383
Municipal securities	193		—		7		186
U.S. Treasury notes	9		—		—		9



Other	46		—		2		44
Total	$	4,459	$	9	$	121	$	4,347


	December 31, 2023
	Amortized Cost		Gross Unrealized				Estimated Fair Value
			Gains		Losses

	(In millions)
Corporate debt securities	$	2,781	$	16	$	65	$	2,732
Mortgage-backed securities	951		4		44		911
Asset-backed securities	376		1		12		365
Municipal securities	172		—		6		166
U.S. Treasury notes	40		—		—		40


Other	47		—		2		45
Total	$	4,367	$	21	$	129	$	4,259


	Amortized Cost		Estimated Fair Value

	(In millions)
Due in one year or less	$	666	$	657
Due after one year through five years	2,273		2,225
Due after five years through ten years	452		446
Due after ten years	1,068		1,019
Total	$	4,459	$	4,347

In the six months ended June 30, 2024, and 2023, maturities and redemptions of available-for-sale securities amounted to $471 million and $292 million, respectively, and sales amounted to $35 million and $254 million, respectively. 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 six months ended June 30, 2024 and 2023. Gross realized investment losses amounted to $3 million and $10 million in the six months ended June 30, 2024 and 2023, respectively, and were reclassified into earnings from other comprehensive income on a net-of-tax basis.

We have determined that unrealized losses at June 30, 2024, and December 31, 2023, 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 realized 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, 2024:


	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	$	648	$	5	421	$	1,524	$	52	725
Mortgage-backed securities	144		2		117	516		43		314
Asset-backed securities	—		—		—	220		10		104
Municipal securities	—		—		—	113		7		108



Other	—		—		—	22		2		21

Total	$	792	$	7	538	$	2,395	$	114	1,272


	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	$	263	$	1	160	$	1,553	$	64	754
Mortgage-backed securities	123		2		98	549		42		283
Asset-backed securities	—		—		—	195		12		91
Municipal securities	—		—		—	117		6		116


Other	—		—		—	17		2		17

Total	$	386	$	3	258	$	2,431	$	126	1,261

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 $268 million at June 30, 2024, of which $184 million will mature in one year or less, $78 million will mature in one through five years, and $6 million will mature after five years.