Retirement Plans and Other Benefits (Tables)

12 Months Ended

Dec. 31, 2015

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
	2015			2014			2013			2015			2014			2013
Service cost-benefits earned during the period	$	59,627		$	53,080		$	64,195		$	16,827		$	18,139		$	23,597
Interest cost on benefit obligation	123,983			129,194			112,392			28,102			41,243			41,536
Expected return on plan assets	(179,231		)	(158,998		)	(146,333		)	(36,855		)	(46,400		)	(45,717		)
Amortization of:
Prior service cost (credit)	594			869			1,097			(37,968		)	(9,626		)	(179		)
Net actuarial loss	31,056			10,963			39,852			4,881			1,175			11,310
Net periodic benefit cost	$	36,029		$	35,108		$	71,203		$	(25,013	)	$	4,531		$	30,547
Portion of cost charged to expense	$	20,036		$	21,985		$	38,968		$	(10,391	)	$	6,000		$	18,469

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 2015 and 2014 (dollars in thousands):

	Pension						Other Benefits
	2015			2014			2015			2014
Change in Benefit Obligation
Benefit obligation at January 1	$	3,078,648		$	2,646,530		$	682,335		$	890,418
Service cost	59,627			53,080			16,827			18,139
Interest cost	123,983			129,194			28,102			41,243
Benefit payments	(137,115		)	(128,550		)	(24,988		)	(29,054		)
Actuarial (gain) loss	(91,340		)	378,394			(55,256		)	150,188
Plan amendments	—			—			—			(388,599		)
Benefit obligation at December 31	3,033,803			3,078,648			647,020			682,335
Change in Plan Assets
Fair value of plan assets at January 1	2,615,404			2,264,121			834,625			748,339
Actual return on plan assets	(44,690		)	292,992			(2,399		)	105,223
Employer contributions	100,000			175,000			791			770
Benefit payments	(127,940		)	(116,709		)	—			(19,707		)
Fair value of plan assets at December 31	2,542,774			2,615,404			833,017			834,625
Funded Status at December 31	$	(491,029	)	$	(463,244	)	$	185,997		$	152,290

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, 2015 and 2014 (dollars in thousands):

	2015		2014
Projected benefit obligation	$	3,033,803	$	3,078,648
Accumulated benefit obligation	2,873,467		2,873,741
Fair value of plan assets	2,542,774		2,615,404

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, 2015 and 2014 (dollars in thousands):

	Pension						Other Benefits
	2015			2014			2015		2014
Noncurrent asset	$	—		$	—		$	185,997	$	152,290
Current liability	(10,031		)	(9,508		)	—		—
Noncurrent liability	(480,998		)	(453,736		)	—		—
Net amount recognized	$	(491,029	)	$	(463,244	)	$	185,997	$	152,290

Schedule of accumulated other comprehensive loss

The following table shows the details related to accumulated other comprehensive loss as of December 31, 2015 and 2014 (dollars in thousands): 

	Pension						Other Benefits
	2015			2014			2015			2014
Net actuarial loss	$	679,501		$	577,976		$	127,124		$	148,006
Prior service cost (credit)	609			1,203			(341,301		)	(379,269		)
APS’s portion recorded as a regulatory (asset) liability	(619,223		)	(485,037		)	213,621			230,916
Income tax expense (benefit)	(23,663		)	(36,890		)	925			851
Accumulated other comprehensive loss	$	37,224		$	57,252		$	369		$	504

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 2016 (dollars in thousands):

	Pension		Other Benefits
Net actuarial loss	$	38,923	$	3,784
Prior service cost (credit)	527		(37,884		)
Total amounts estimated to be amortized from accumulated other comprehensive loss (gain) and regulatory assets (liabilities) in 2016	$	39,450	$	(34,100	)

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,
	2015		2014		2015		2014				2013
							January - September		October - December
Discount rate – pension	4.37	%	4.02	%	4.02	%	4.88	%	4.88	%	4.01	%
Discount rate – other benefits	4.52	%	4.14	%	4.14	%	5.10	%	4.41	%	4.20	%
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	%	7.00	%
Expected long-term return on plan assets - other benefits	N/A		N/A		4.45	%	6.80	%	4.25	%	7.00	%
Initial healthcare cost trend rate (pre-65 participants)	7.00	%	7.00	%	7.00	%	7.50	%	7.50	%	7.50	%
Initial healthcare cost trend rate (post-65 participants)	5.00	%	5.00	%	5.00	%	7.50	%	5.00	%	7.50	%
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		4		0		4

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	$	8,834	$	(5,890	)
Effect on service and interest cost components of net periodic other postretirement benefit costs	9,069		(6,949		)
Effect on the accumulated other postretirement benefit obligation	100,322		(80,332		)

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, 2014, 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)		Significant Unobservable Inputs (Level 3)		Other (b)		Balance at December 31, 2014
Pension Plan:
Assets:
Cash and cash equivalents	$	387	$	—	$	—	$	—	$	387
Fixed Income Securities:
Corporate	—		1,162,096		—		—		1,162,096
U.S. Treasury	291,817		—		—		—		291,817
Other (a)	—		113,265		—		—		113,265
Equities:
U.S. Companies	246,387		—		—		—		246,387
International Companies	18,069		—		—		—		18,069
Common and collective trusts:
U.S. Equities	—		127,336		—		—		127,336
International Equities	—		317,167		—		—		317,167
Real estate	—		129,715		—		—		129,715
Partnerships	—		138,337		27,929		—		166,266
Short-term investments and other	—		26,016		—		16,883		42,899
Total Pension Plan	$	556,660	$	2,013,932	$	27,929	$	16,883	$	2,615,404
Other Benefits:
Assets:
Cash and cash equivalents	$	318	$	—	$	—	$	—	$	318
Fixed Income Securities:
Corporate	—		187,961		—		—		187,961
U.S. Treasury	130,967		—		—		—		130,967
Other (a)	—		35,291		—		—		35,291
Equities:
U.S. Companies	265,106		—		—		—		265,106
International Companies	17,813		—		—		—		17,813
Common and collective trusts:
U.S. Equities	—		88,258		—		—		88,258
International Equities	—		85,746		—		—		85,746
Real Estate	—		11,657		—		—		11,657
Short-term investments and other	—		7,408		—		4,100		11,508
Total Other Benefits	$	414,204	$	416,321	$	—	$	4,100	$	834,625

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

(b) Represents plan receivables and payables.

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)		Significant Unobservable Inputs (Level 3)		Other (b)		Balance at December 31, 2015
Pension Plan:
Assets:
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 (a)	—		113,008		—		—		113,008
Equities:
U.S. companies	233,021		—		—		—		233,021
International companies	14,680		—		—		—		14,680
Common and collective trusts:
U.S. equities	—		130,097		—		—		130,097
International equities	—		185,892		—		—		185,892
Real estate	—		150,359		—		—		150,359
Partnerships	—		127,840		42,097		—		169,937
Mutual funds - International equities	116,307		—		—		—		116,307
Short-term investments and other	—		29,599		—		14,467		44,066
Total Pension Plan	$	640,679	$	1,845,531	$	42,097	$	14,467	$	2,542,774
Other Benefits:
Assets:
Cash and cash equivalents	$	240	$	—	$	—	$	—	$	240
Fixed income securities:
Corporate	—		217,026		—		—		217,026
U.S. Treasury	131,435		—		—		—		131,435
Other (a)	—		31,106		—		—		31,106
Equities:
U.S. companies	253,193		—		—		—		253,193
International companies	12,390		—		—		—		12,390
Common and collective trusts:
U.S. equities	—		81,516		—		—		81,516
International equities	—		28,539		—		—		28,539
Real estate	—		13,512		—		—		13,512
Mutual funds - International equities	52,568		—		—		—		52,568
Short-term investments and other	5,065		3,331		—		3,096		11,492
Total Other Benefits	$	454,891	$	375,030	$	—	$	3,096	$	833,017

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

(b) Represents plan receivables and payables.

Schedule of changes in fair value for assets that are measured at fair value on a recurring basis using significant unobservable inputs (Level 3)

The following table shows the changes in fair value for assets that are measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the year ended December 31, 2015 and 2014 (dollars in thousands):

	Pension
Partnerships	2015			2014
Beginning balance at January 1	$	27,929		$	8,660
Actual return on assets still held at December 31	2,789			927
Purchases	13,187			19,984
Sales	(1,808		)	(1,642		)
Transfers in and/or out of Level 3	—			—
Ending balance at December 31	$	42,097		$	27,929

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
2016	$	152,146	$	26,468
2017	171,005		28,444
2018	170,534		30,490
2019	180,700		32,438
2020	188,988		33,982
Years 2021-2025	1,023,451		184,335