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

9 Months Ended

Sep. 30, 2023

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, 2023
	Fair Value							Total Unrealized Gains		Total Unrealized Losses
Investment Type:	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
Equity securities	$	444,063	$	55,253	$	499,316		$	327,887	$	(23)
Available for sale-fixed income securities	693,510		311,624		1,005,134		(a)	623		(74,383)
Other	(17,110)		1,282		(15,828)		(b)	—		—
Total	$	1,120,463	$	368,159	$	1,488,622		$	328,510	$	(74,406)

(a)As of September 30, 2023, the amortized cost basis of these available-for-sale investments is $1,079 million.

(b)Represents net pending securities sales and purchases.

	December 31, 2022
	Fair Value							Total Unrealized Gains		Total Unrealized Losses
Investment Type:	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
Equity securities	$	487,240	$	66,974	$	554,214		$	334,817	$	(267)
Available for sale-fixed income securities	582,343		279,294		861,637		(a)	3,177		(68,795)
Other	3,827		963		4,790		(b)	—		(29)
Total	$	1,073,410	$	347,231	$	1,420,641		$	337,994	$	(69,091)

(a)As of December 31, 2022, the amortized cost basis of these available-for-sale investments is $927 million.

(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
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
2022
Realized gains	$	788	$	—	$	788
Realized losses	(6,908)		—		(6,908)
Proceeds from the sale of securities (a)	153,573		65,244		218,817

(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.

	Nine Months Ended September 30,
	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
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
2022
Realized gains	$	8,093	$	—	$	8,093
Realized losses	(26,582)		—		(26,582)
Proceeds from the sale of securities (a)	783,232		127,255		910,487

(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, 2023, is as follows (dollars in thousands):

	Nuclear Decommissioning Trusts		Coal Reclamation Escrow Account		Active Union Employee Medical Account		Total
Less than one year	$	18,012	$	59,191	$	18,891	$	96,094
1 year – 5 years	194,625		42,158		184,682		421,465
5 years – 10 years	163,662		—		2,788		166,450
Greater than 10 years	317,211		3,914		—		321,125
Total	$	693,510	$	105,263	$	206,361	$	1,005,134