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

12 Months Ended

Dec. 31, 2019

Investments, Debt and Equity Securities [Abstract]

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 trust and other special use fund assets at December 31, 2019 and December 31, 2018 (dollars in thousands): 

	December 31, 2019
	Fair Value							Total Unrealized Gains		Total Unrealized Losses
Investment Type:	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
Equity Securities	$	529,716	$	7,142	$	536,858		$	337,681	$	—
Available for Sale-Fixed Income Securities	478,658		237,479		716,137		(a)	25,795		(669		)
Other	2,401		474		2,875		(b)	—		—
Total	$	1,010,775	$	245,095	$	1,255,870		$	363,476	$	(669	)

(a) As of December 31, 2019, the amortized cost basis of these available-for-sale investments is $691 million.

(b) Represents net pending securities sales and purchases.

	December 31, 2018
	Fair Value							Total Unrealized Gains		Total Unrealized Losses
Investment Type:	Nuclear Decommissioning Trusts		Other Special Use Funds		Total
Equity Securities	$	402,008	$	45,130	$	447,138		$	222,147	$	(459	)
Available for Sale-Fixed Income Securities	446,978		190,378		637,356		(a)	8,634		(6,778		)
Other	2,148		593		2,741		(b)	—		—
Total	$	851,134	$	236,101	$	1,087,235		$	230,781	$	(7,237	)

(a) As of December 31, 2018, the amortized cost basis of these available-for-sale investments is $635 million.

(b)

Represents net pending securities sales and purchases.

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 for the years ended December 31, 2019, 2018 and 2017 (dollars in thousands):

	Year Ended December 31,
	Nuclear Decommissioning Trusts			Other Special Use Funds			Total
2019
Realized gains	$	11,024		$	108		$	11,132
Realized losses	(6,972		)	—			(6,972		)
Proceeds from the sale of securities (a)	473,806			245,228			719,034
2018
Realized gains	6,679			1			6,680
Realized losses	(13,552		)	—			(13,552		)
Proceeds from the sale of securities (a)	554,385			98,648			653,033
2017
Realized gains	21,813			17			21,830
Realized losses	(13,146		)	(9		)	(13,155		)
Proceeds from the sale of securities (a)	542,246			4,093			546,339

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

Fair value of fixed income securities, summarized by contractual maturities

The fair value of fixed income securities, summarized by contractual maturities, at December 31, 2019 is as follows (dollars in thousands):

	Nuclear Decommissioning Trusts		Coal Reclamation Escrow Account		Active Union Medical Trust		Total
Less than one year	$	26,984	$	31,953	$	40,449	$	99,386
1 year – 5 years	136,139		25,229		138,042		299,410
5 years – 10 years	105,797		—		—		105,797
Greater than 10 years	209,738		1,806		—		211,544
Total	$	478,658	$	58,988	$	178,491	$	716,137