Nuclear Decommissioning Trusts (Tables)

12 Months Ended

Dec. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Fair value of APS's nuclear decommissioning trust fund assets

The following table includes the unrealized gains and losses based on the original cost of the investment and summarizes the fair value of APS’s nuclear decommissioning trust fund assets at December 31, 2015 and December 31, 2014 (dollars in thousands):

	Fair Value			Total  Unrealized  Gains		Total  Unrealized  Losses
December 31, 2015
Equity securities	$	314,957		$	157,098	$	(115	)
Fixed income securities	420,574			11,955		(2,645		)
Net payables (a)	(335		)	—		—
Total	$	735,196		$	169,053	$	(2,760	)

	Fair Value			Total  Unrealized  Gains		Total  Unrealized  Losses
December 31, 2014
Equity securities	$	309,620		$	159,274	$	(15	)
Fixed income securities	411,491			17,260		(1,073		)
Net payables (a)	(7,245		)	—		—
Total	$	713,866		$	176,534	$	(1,088	)

(a) Net payables relate to pending purchases and sales of securities.

Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds

The following table sets forth approximate gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds (dollars in thousands):

	Year Ended December 31,
	2015			2014			2013
Realized gains	$	5,189		$	4,725		$	5,459
Realized losses	(6,225		)	(4,525		)	(6,706		)
Proceeds from the sale of securities (a)	478,813			356,195			446,025

(a) Proceeds are reinvested in the 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, 2015 is as follows (dollars in thousands):

	Fair Value
Less than one year	$	14,001
1 year – 5 years	117,356
5 years – 10 years	114,769
Greater than 10 years	174,448
Total	$	420,574