Retirement Plans and Other Benefits (Tables)

12 Months Ended

Dec. 31, 2016

Compensation and Retirement Disclosure [Abstract]

Schedule of net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction, billed to electric plant participants or charged or amortized to the regulatory asset)

The following table provides details of the plans’ net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction, billed to electric plant participants or charged to the regulatory asset or liability) (dollars in thousands):

	Pension									Other Benefits
	2016			2015			2014			2016			2015			2014
Service cost-benefits earned during the period	$	53,792		$	59,627		$	53,080		$	14,993		$	16,827		$	18,139
Interest cost on benefit obligation	131,647			123,983			129,194			29,721			28,102			41,243
Expected return on plan assets	(173,906		)	(179,231		)	(158,998		)	(36,495		)	(36,855		)	(46,400		)
Amortization of:
Prior service cost (credit)	527			594			869			(37,883		)	(37,968		)	(9,626		)
Net actuarial loss	40,717			31,056			10,963			4,589			4,881			1,175
Net periodic benefit cost	$	52,777		$	36,029		$	35,108		$	(25,075	)	$	(25,013	)	$	4,531
Portion of cost charged to expense	$	26,172		$	20,036		$	21,985		$	(12,435	)	$	(10,391	)	$	6,000

Schedule of changes in the benefit obligations and funded status

The following table shows the plans’ changes in the benefit obligations and funded status for the years 2016 and 2015 (dollars in thousands):

	Pension						Other Benefits
	2016			2015			2016			2015
Change in Benefit Obligation
Benefit obligation at January 1	$	3,033,803		$	3,078,648		$	647,020		$	682,335
Service cost	53,792			59,627			14,993			16,827
Interest cost	131,647			123,983			29,721			28,102
Benefit payments	(142,247		)	(137,115		)	(26,231		)	(24,988		)
Actuarial (gain) loss	127,467			(91,340		)	50,942			(55,256		)
Benefit obligation at December 31	3,204,462			3,033,803			716,445			647,020
Change in Plan Assets
Fair value of plan assets at January 1	2,542,774			2,615,404			833,017			834,625
Actual return on plan assets	166,408			(44,690		)	63,463			(2,399		)
Employer contributions	100,000			100,000			819			791
Benefit payments	(133,825		)	(127,940		)	(14,648		)	—
Fair value of plan assets at December 31	2,675,357			2,542,774			882,651			833,017
Funded Status at December 31	$	(529,105	)	$	(491,029	)	$	166,206		$	185,997

Schedule of projected benefit obligation and the accumulated benefit obligation for pension plans with an accumulated obligation in excess of plan assets

The following table shows the projected benefit obligation and the accumulated benefit obligation for pension plans with an accumulated obligation in excess of plan assets as of December 31, 2016 and 2015 (dollars in thousands):

	2016		2015
Projected benefit obligation	$	3,204,462	$	3,033,803
Accumulated benefit obligation	3,049,406		2,873,467
Fair value of plan assets	2,675,357		2,542,774

Schedule of amounts recognized on the Consolidated Balance Sheets

The following table shows the amounts recognized on the Consolidated Balance Sheets as of December 31, 2016 and 2015 (dollars in thousands):

	Pension						Other Benefits
	2016			2015			2016		2015
Noncurrent asset	$	—		$	—		$	166,206	$	185,997
Current liability	(19,795		)	(10,031		)	—		—
Noncurrent liability	(509,310		)	(480,998		)	—		—
Net amount recognized	$	(529,105	)	$	(491,029	)	$	166,206	$	185,997

Schedule of accumulated other comprehensive loss

The following table shows the details related to accumulated other comprehensive loss as of December 31, 2016 and 2015 (dollars in thousands): 

	Pension						Other Benefits
	2016			2015			2016			2015
Net actuarial loss	$	773,750		$	679,501		$	146,509		$	127,124
Prior service cost (credit)	81			609			(303,417		)	(341,301		)
APS’s portion recorded as a regulatory (asset) liability	(711,059		)	(619,223		)	156,575			213,621
Income tax expense (benefit)	(24,202		)	(23,663		)	833			925
Accumulated other comprehensive loss	$	38,570		$	37,224		$	500		$	369

Schedule of estimated amounts that will be amortized from accumulated other comprehensive loss and regulatory assets into net periodic benefit cost

The following table shows the estimated amounts that will be amortized from accumulated other comprehensive loss and regulatory assets and liabilities into net periodic benefit cost in 2017 (dollars in thousands):

	Pension		Other Benefits
Net actuarial loss	$	46,971	$	5,181
Prior service cost (credit)	81		(37,842		)
Total amounts estimated to be amortized from accumulated other comprehensive loss (gain) and regulatory assets (liabilities) in 2017	$	47,052	$	(32,661	)

Schedule of weighted-average assumptions used for both the pension and other benefits to determine benefit obligations and net periodic benefit costs

The following table shows the weighted-average assumptions used for both the pension and other benefits to determine benefit obligations and net periodic benefit costs:

	Benefit Obligations As of December 31,				Benefit Costs For the Years Ended December 31,
	2016		2015		2016		2015		2014
									January - September		October - December
Discount rate – pension	4.08	%	4.37	%	4.37	%	4.02	%	4.88	%	4.88	%
Discount rate – other benefits	4.17	%	4.52	%	4.52	%	4.14	%	5.10	%	4.41	%
Rate of compensation increase	4.00	%	4.00	%	4.00	%	4.00	%	4.00	%	4.00	%
Expected long-term return on plan assets - pension	N/A		N/A		6.90	%	6.90	%	6.90	%	6.90	%
Expected long-term return on plan assets - other benefits	N/A		N/A		4.45	%	4.45	%	6.80	%	4.25	%
Initial healthcare cost trend rate (pre-65 participants)	7.00	%	7.00	%	7.00	%	7.00	%	7.50	%	7.50	%
Initial healthcare cost trend rate (post-65 participants)	5.00	%	5.00	%	5.00	%	5.00	%	7.50	%	5.00	%
Ultimate healthcare cost trend rate	5.00	%	5.00	%	5.00	%	5.00	%	5.00	%	5.00	%
Number of years to ultimate trend rate (pre-65 participants)	4		4		4		4		4		4
Number of years to ultimate trend rate (post-65 participants)	0		0		0		0		4		0

Schedule of effects of one percentage point change in the assumed initial and ultimate health care cost trend rates

A one percentage point change in the assumed initial and ultimate healthcare cost trend rates would have the following effects (dollars in thousands): 

	1% Increase		1% Decrease
Effect on other postretirement benefits expense, after consideration of amounts capitalized or billed to electric plant participants	$	8,430	$	(5,455	)
Effect on service and interest cost components of net periodic other postretirement benefit costs	8,440		(6,527		)
Effect on the accumulated other postretirement benefit obligation	108,046		(86,651		)

Schedule of fair value of pension plan and other postretirement benefit plan assets, by asset category

The fair value of Pinnacle West’s pension plan and other postretirement benefit plan assets at December 31, 2015, by asset category, are as follows (dollars in thousands):

	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Other (a)		Balance at December 31, 2015
Pension Plan:
Cash and cash equivalents	$	1,893	$	—	$	—	$	1,893
Fixed Income Securities:
Corporate	—		1,108,736		—		1,108,736
U.S. Treasury	274,778		—		—		274,778
Other (b)	—		113,008		—		113,008
Common stock equities (c)	247,701		—		—		247,701
Mutual funds - International equities	116,307		—		—		116,307
Common and collective trusts:
Equities	—		—		315,989		315,989
Real Estate	—		—		150,359		150,359
Partnerships	—		—		169,937		169,937
Short-term investments and other (d)	—		—		44,066		44,066
Total	$	640,679	$	1,221,744	$	680,351	$	2,542,774
Other Benefits:
Cash and cash equivalents	$	240	$	—	$	—	$	240
Fixed Income Securities:
Corporate	—		217,026		—		217,026
U.S. Treasury	131,435		—		—		131,435
Other (b)	—		31,106		—		31,106
Common stock equities (c)	265,583		—		—		265,583
Mutual funds - International equities	52,568		—		—		52,568
Common and collective trusts:
Equities	—		—		110,055		110,055
Real Estate	—		—		13,512		13,512
Short-term investments and other (d)	—		—		11,492		11,492
Total	$	449,826	$	248,132	$	135,059	$	833,017

(a) These investments primarily represent assets valued using net asset value as a practical expedient, and have not been classified in the fair value hierarchy.

(b) This category consists primarily of debt securities issued by municipalities.

(c) This category primarily consists of US common stock equities.

(d) This category includes plan receivables and payables.

The fair value of Pinnacle West’s pension plan and other postretirement benefit plan assets at December 31, 2016, by asset category, are as follows (dollars in thousands):

	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Other (a)		Balance at December 31, 2016
Pension Plan:
Cash and cash equivalents	$	13,995	$	—	$	—	$	13,995
Fixed income securities:
Corporate	—		1,210,453		—		1,210,453
U.S. Treasury	112,583		—		—		112,583
Other (b)	—		102,170		—		102,170
Common stock equities (c)	235,109		—		—		235,109
Mutual funds (d)	251,506		—		—		251,506
Common and collective trusts:
Equities	—		—		266,840		266,840
Real estate	—		—		161,449		161,449
Partnerships	—		—		208,915		208,915
Short-term investments and other (e)	—		—		112,337		112,337
Total	$	613,193	$	1,312,623	$	749,541	$	2,675,357
Other Benefits:
Cash and cash equivalents	$	304	$	—	$	—	$	304
Fixed income securities:
Corporate	—		268,193		—		268,193
U.S. Treasury	145,255		—		—		145,255
Other (b)	—		34,506		—		34,506
Common stock equities (c)	243,741		—		—		243,741
Mutual funds (d)	67,418		—		—		67,418
Common and collective trusts:
Equities	—		—		95,814		95,814
Real estate	—		—		14,509		14,509
Partnerships	—		—		3,060		3,060
Short-term investments and other (e)	—		—		9,851		9,851
Total	$	456,718	$	302,699	$	123,234	$	882,651

(a) These investments primarily represent assets valued using net asset value as a practical expedient, and have not been classified in the fair value hierarchy.

(b) This category consists primarily of debt securities issued by municipalities.

(c) This category primarily consists of US common stock equities.

(d) These funds invest in US and international common stock equities.

(e) This category includes plan receivables and payables.

Schedule of estimated future benefit payments, which reflect estimated future employee service, for the next five years and the succeeding five years thereafter

Benefit payments, which reflect estimated future employee service, for the next five years and the succeeding five years thereafter, are estimated to be as follows (dollars in thousands):

Year	Pension		Other Benefits
2017	$	172,859	$	31,126
2018	173,232		33,795
2019	182,944		36,195
2020	191,037		37,998
2021	196,292		39,368
Years 2022-2026	1,049,149		201,944