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

3 Months Ended

Mar. 31, 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):  

	March 31, 2024
	Fair Value							Total Unrealized Gains		Total Unrealized Losses
Investment Type:	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
Equity securities	$	394,277	$	46,665	$	440,942		$	325,101	$	—
Available for sale-fixed income securities	842,618		316,137		1,158,755		(a)	12,056		(48,075)
Other	2,129		1,423		3,552		(b)	164		—
Total	$	1,239,024	$	364,225	$	1,603,249		$	337,321	$	(48,075)

(a)As of March 31, 2024, the amortized cost basis of these available-for-sale investments is $1,194,000 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 March 31,
	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
2024
Realized gains	$	54,492	$	80	$	54,572
Realized losses	$	(2,815)	$	—	$	(2,815)
Proceeds from the sale of securities (a)	$	377,822	$	66,048	$	443,870
2023
Realized gains	$	1,210	$	—	$	1,210
Realized losses	$	(5,694)	$	—	$	(5,694)
Proceeds from the sale of securities (a)	$	136,185	$	90,441	$	226,626

(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 March 31, 2024, is as follows (dollars in thousands):

	Nuclear Decommissioning Trusts		Coal Reclamation Escrow Account		Active Union Employee Medical Account		Total
Less than one year	$	24,043	$	59,198	$	37,081	$	120,322
1 year – 5 years	254,711		43,219		151,844		449,774
5 years – 10 years	193,975		—		24,795		218,770
Greater than 10 years	369,889		—		—		369,889
Total	$	842,618	$	102,417	$	213,720	$	1,158,755