Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Tables)

9 Months Ended

Sep. 30, 2024

Investments, Debt and Equity Securities [Abstract]

Schedule of Fair Value of APS's Nuclear Decommissioning Trust Fund Assets

The following tables present the unrealized gains and losses based on the original cost of the investment and summarizes the fair value of APS’s nuclear decommissioning trusts and other special use fund assets (dollars in thousands):  

	September 30, 2024
	Fair Value							Total Unrealized Gains		Total Unrealized Losses
Investment Type:	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
Equity securities	$	430,217	$	53,976	$	484,193		$	353,327	$	—
Available for sale-fixed income securities	868,187		331,763		1,199,950		(a)	28,894		(22,091)
Other	1,608		1,760		3,368		(b)	472		—
Total	$	1,300,012	$	387,499	$	1,687,511		$	382,693	$	(22,091)

(a)As of September 30, 2024, the amortized cost basis of these available-for-sale investments is $1,193,419 thousand.

(b)Represents net pending securities sales and purchases.

	December 31, 2023
	Fair Value							Total Unrealized Gains		Total Unrealized Losses
Investment Type:	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
Equity securities	$	420,680	$	40,991	$	461,671		$	336,555	$	—
Available for sale-fixed income securities	781,333		319,594		1,100,927		(a)	21,518		(40,868)
Other	(767)		2,196		1,429		(b)	39		—
Total	$	1,201,246	$	362,781	$	1,564,027		$	358,112	$	(40,868)

(a)As of December 31, 2023, the amortized cost basis of these available-for-sale investments is $1,120,000 thousand.

(b)Represents net pending securities sales and purchases.

Schedule of Realized Gains and Losses and Proceeds from the Sale of Securities by the Nuclear Decommissioning Trust Funds

The following table sets forth APS’s realized gains and losses relating to the sale and maturity of available-for-sale debt securities and equity securities, and the proceeds from the sale and maturity of these investment securities (dollars in thousands):

	Three Months Ended September 30,
	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
2024
Realized gains	$	3,825	$	—	$	3,825
Realized losses	$	(4,162)	$	—	$	(4,162)
Proceeds from the sale of securities (a)	$	293,758	$	74,238	$	367,996
2023
Realized gains	$	34,897	$	—	$	34,897
Realized losses	$	(11,568)	$	(547)	$	(12,115)
Proceeds from the sale of securities (a)	$	487,324	$	90,816	$	578,140

(a)    Proceeds are reinvested in the nuclear decommissioning trusts and other special use funds, excluding investment fees and amounts reimbursed to the Company for active union employee medical claims from the active union employee medical account.

	Nine Months Ended September 30,
	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
2024
Realized gains	$	67,260	$	80	$	67,340
Realized losses	$	(10,683)	$	—	$	(10,683)
Proceeds from the sale of securities (a)	$	942,211	$	198,160	$	1,140,371
2023
Realized gains	$	71,338	$	—	$	71,338
Realized losses	$	(28,454)	$	(547)	$	(29,001)
Proceeds from the sale of securities (a)	$	922,270	$	223,398	$	1,145,668

(a)    Proceeds are reinvested in the nuclear decommissioning trusts and other special use funds, excluding amounts reimbursed to the Company for active union employee medical claims from the active union employee medical account.

Schedule of Fair Value of Fixed Income Securities, Summarized by Contractual Maturities

The fair value of APS’s fixed income securities, summarized by contractual maturities, at September 30, 2024, is as follows (dollars in thousands):

	Nuclear Decommissioning Trusts		Coal Reclamation Escrow Account		Active Union Employee Medical Account		Total
Less than one year	$	30,015	$	62,874	$	76,554	$	169,443
1 year – 5 years	269,541		48,840		143,495		461,876
5 years – 10 years	197,500		—		—		197,500
Greater than 10 years	371,131		—		—		371,131
Total	$	868,187	$	111,714	$	220,049	$	1,199,950