Benefit Plans and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2013

Benefit Plans and Other Postretirement Benefits [Abstract]

Projected Benefit Payments for the Pension and Postretirement Benefit Plans

Projected Benefit Payments — The following table lists SPS’ projected benefit payments for the pension and postretirement benefit plans:

(Thousands of Dollars)	Projected Pension Benefit Payments		Gross Projected Postretirement Health Care Benefit Payments		Expected Medicare Part D Subsidies		Net Projected Postretirement Health Care Benefit Payments
2014	$	26,265	$	3,285	$	33	$	3,252
2015	27,361		3,450		36		3,414
2016	27,565		3,547		50		3,497
2017	28,738		3,691		52		3,639
2018	29,703		3,582		55		3,527
2019-2023	153,507		17,912		186		17,726

Pension Plans

Benefit Plans and Other Postretirement Benefits [Abstract]

Target Asset Allocations and Plan Assets Measured at Fair Value

The following tables present, for each of the fair value hierarchy levels, SPS’ pension plan assets that are measured at fair value as of Dec. 31, 2013 and 2012:

	Dec. 31, 2013
(Thousands of Dollars)	Level 1		Level 2		Level 3		Total
Cash equivalents	$	17,354	$	—	$	—	$	17,354
Derivatives	—		4,200		—		4,200
Government securities	—		26,649		—		26,649
Corporate bonds	—		79,635		—		79,635
Asset-backed securities	—		889		—		889
Mortgage-backed securities	—		1,939		—		1,939
Common stock	12,813		—		—		12,813
Private equity investments	—		—		18,222		18,222
Commingled funds	—		223,322		—		223,322
Real estate	—		—		5,755		5,755
Securities lending collateral obligation and other	—		2,615		—		2,615
Total	$	30,167	$	339,249	$	23,977	$	393,393

	Dec. 31, 2012
(Thousands of Dollars)	Level 1		Level 2			Level 3		Total
Cash equivalents	$	26,765	$	—		$	—	$	26,765
Derivatives	—		1,388			—		1,388
Government securities	—		33,676			—		33,676
Corporate bonds	—		95,726			—		95,726
Asset-backed securities	—		—			1,755		1,755
Mortgage-backed securities	—		—			4,331		4,331
Common stock	7,762		—			—		7,762
Private equity investments	—		—			17,049		17,049
Commingled funds	—		183,957			—		183,957
Real estate	—		—			6,969		6,969
Securities lending collateral obligation and other	—		(3,240		)	—		(3,240		)
Total	$	34,527	$	311,507		$	30,104	$	376,138

The following table presents the target pension asset allocations for SPS:

	2013		2012
Domestic and international equity securities	29	%	21	%
Long-duration fixed income and interest rate swap securities	36		50
Short-to-intermediate term fixed income securities	14		8
Alternative investments	19		19
Cash	2		2
Total	100	%	100	%

Changes in Level 3 Plan Assets

The following tables present the changes in SPS’ Level 3 pension plan assets for the years ended Dec. 31, 2013, 2012 and 2011:

(Thousands of Dollars)	Jan. 1, 2013		Net Realized Gains (Losses)			Net Unrealized Gains (Losses)			Purchases, Issuances and Settlements, Net			Transfers Out of Level 3 (a)			Dec. 31, 2013
Asset-backed securities	$	1,755	$	—		$	—		$	—		$	(1,755	)	$	—
Mortgage-backed securities	4,331		—			—			—			(4,331		)	—
Private equity investments	17,049		2,630			(1,055		)	(402		)	—			18,222
Real estate	6,969		(322		)	1,475			1,128			(3,495		)	5,755
Total	$	30,104	$	2,308		$	420		$	726		$	(9,581	)	$	23,977

^(a) Transfers out of Level 3 into Level 2 were principally due to diminished use of unobservable inputs that were previously significant to these fair value measurements and were subsequently sold during 2013.

(Thousands of Dollars)	Jan. 1, 2012		Net Realized Gains (Losses)		Net Unrealized Gains (Losses)			Purchases, Issuances and Settlements, Net			Transfers Out of Level 3		Dec. 31, 2012
Asset-backed securities	$	4,018	$	531	$	(741	)	$	(2,053	)	$	—	$	1,755
Mortgage-backed securities	7,907		245		(265		)	(3,556		)	—		4,331
Private equity investments	16,159		1,886		(2,296		)	1,300			—		17,049
Real estate	3,586		2		551			2,830			—		6,969
Total	$	31,670	$	2,664	$	(2,751	)	$	(1,479	)	$	—	$	30,104

(Thousands of Dollars)	Jan. 1, 2011		Net Realized Gains (Losses)			Net Unrealized Gains (Losses)			Purchases, Issuances and Settlements, Net			Transfers Out of Level 3		Dec. 31, 2011
Asset-backed securities	$	3,450	$	328		$	(355	)	$	595		$	—	$	4,018
Mortgage-backed securities	11,060		170			(865		)	(2,458		)	—		7,907
Private equity investments	11,464		401			1,300			2,994			—		16,159
Real estate	10,132		(61		)	3,131			(9,616		)	—		3,586
Total	$	36,106	$	838		$	3,211		$	(8,485	)	$	—	$	31,670

Change in Projected Benefit Obligation

Benefit Obligations — A comparison of the actuarially computed pension benefit obligation and plan assets for SPS is presented in the following table:

(Thousands of Dollars)	2013			2012
Accumulated Benefit Obligation at Dec. 31	$	402,509		$	416,808
Change in Projected Benefit Obligation:
Obligation at Jan. 1	$	454,184		$	403,367
Service cost	9,615			8,520
Interest cost	17,908			19,697
Plan amendments	—			98
Actuarial (gain) loss	(27,185		)	45,881
Transfer from other plan	3,625			—
Benefit payments	(23,840		)	(23,379		)
Obligation at Dec. 31	$	434,307		$	454,184

Change in Fair Value of Plan Assets

(Thousands of Dollars)	2013			2012
Change in Fair Value of Plan Assets:
Fair value of plan assets at Jan. 1	$	376,138		$	350,054
Actual return on plan assets	15,455			36,403
Employer contributions	22,015			13,060
Transfer from other plan	3,625			—
Benefit payments	(23,840		)	(23,379		)
Fair value of plan assets at Dec. 31	$	393,393		$	376,138

Funded Status of Plans

(Thousands of Dollars)	2013			2012
Funded Status of Plans at Dec. 31:
Funded status (a)	$	(40,914	)	$	(78,046	)

^(a)  Amounts are recognized in noncurrent liabilities on SPS’ balance sheets.

Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost

(Thousands of Dollars)	2013		2012
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost:
Net loss	$	208,594	$	244,412
Prior service cost	93		963
Total	$	208,687	$	245,375

Amounts Not Yet Recognized as Components of Net Periodic Benefit Costs Recorded on the Balance Sheet Based Upon Expected Recovery in Rates

(Thousands of Dollars)	2013		2012
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates:
Current regulatory assets	$	15,843	$	14,877
Noncurrent regulatory assets	192,844		230,498
Total	$	208,687	$	245,375

Schedule of Assumptions Used

	2013		2012		2011
Significant Assumptions Used to Measure Costs:
Discount rate	4.00	%	5.00	%	5.50	%
Expected average long-term increase in compensation level	3.75		4.00		4.00
Expected average long-term rate of return on assets	6.49		6.68		6.80

Measurement date Dec. 31, 2013 Dec. 31, 2012

	2013		2012
Significant Assumptions Used to Measure Benefit Obligations:
Discount rate for year-end valuation	4.75	%	4.00	%
Expected average long-term increase in compensation level	3.75		3.75
Mortality table	RP 2000		RP 2000

Components of Net Periodic Benefit Costs

Benefit Costs —The components of SPS’ net periodic pension cost were:

(Thousands of Dollars)	2013			2012			2011
Service cost	$	9,615		$	8,520		$	7,690
Interest cost	17,908			19,697			20,036
Expected return on plan assets	(23,970		)	(24,928		)	(26,316		)
Amortization of prior service cost	870			1,438			1,505
Amortization of net loss	17,148			12,897			9,046
Net periodic pension cost	$	21,571		$	17,624		$	11,961
Costs not recognized due to effects of regulation	(1,269		)	(4,300		)	(2,300		)
Net benefit cost recognized for financial reporting	$	20,302		$	13,324		$	9,661

Postretirement Benefit Plan

Benefit Plans and Other Postretirement Benefits [Abstract]

Target Asset Allocations and Plan Assets Measured at Fair Value

The following tables present, for each of the fair value hierarchy levels, SPS’ postretirement benefit plan assets that are measured at fair value as of Dec. 31, 2013 and 2012:

	Dec. 31, 2013
(Thousands of Dollars)	Level 1		Level 2			Level 3		Total
Cash equivalents	$	1,941	$	—		$	—	$	1,941
Derivatives	—		(38		)	—		(38		)
Government securities	—		5,549			—		5,549
Insurance contracts	—		5,016			—		5,016
Corporate bonds	—		4,926			—		4,926
Asset-backed securities	—		319			—		319
Mortgage-backed securities	—		2,303			—		2,303
Commingled funds	—		28,331			—		28,331
Other	—		(1,609		)	—		(1,609		)
Total	$	1,941	$	44,797		$	—	$	46,738

	Dec. 31, 2012
(Thousands of Dollars)	Level 1		Level 2			Level 3		Total
Cash equivalents	$	8,774	$	—		$	—	$	8,774
Government securities	—		7,061			—		7,061
Insurance contracts	—		4,807			—		4,807
Corporate bonds	—		4,211			—		4,211
Asset-backed securities	—		—			73		73
Mortgage-backed securities	—		—			3,841		3,841
Commingled funds	—		21,958			—		21,958
Other	—		(4,503		)	—		(4,503		)
Total	$	8,774	$	33,534		$	3,914	$	46,222

Changes in Level 3 Plan Assets

The following tables present the changes in SPS’ Level 3 postretirement benefit plan assets for the years ended Dec. 31, 2013, 2012 and 2011:

(Thousands of Dollars)	Jan. 1, 2013		Net Realized Gains (Losses)		Net Unrealized Gains (Losses)		Purchases, Issuances and Settlements, Net		Transfers Out of Level 3 (a)			Dec. 31, 2013
Asset-backed securities	$	73	$	—	$	—	$	—	$	(73	)	$	—
Mortgage-backed securities	3,841		—		—		—		(3,841		)	—
Total	$	3,914	$	—	$	—	$	—	$	(3,914	)	$	—

^(a) Transfers out of Level 3 into Level 2 were principally due to diminished use of unobservable inputs that were previously significant to these fair value measurements and were subsequently sold during 2013.

(Thousands of Dollars)	Jan. 1, 2012		Net Realized Gains (Losses)			Net Unrealized Gains (Losses)		Purchases, Issuances and Settlements, Net			Transfers Out of Level 3		Dec. 31, 2012
Asset-backed securities	$	730	$	(32	)	$	179	$	(804	)	$	—	$	73
Mortgage-backed securities	2,535		(70		)	377		999			—		3,841
Total	$	3,265	$	(102	)	$	556	$	195		$	—	$	3,914

(Thousands of Dollars)	Jan. 1, 2011		Net Realized Gains (Losses)			Net Unrealized Gains (Losses)			Purchases, Issuances and Settlements, Net		Transfers Out of Level 3		Dec. 31, 2011
Asset-backed securities	$	245	$	(2	)	$	(101	)	$	588	$	—	$	730
Mortgage-backed securities	1,820		(157		)	194			678		—		2,535
Total	$	2,065	$	(159	)	$	93		$	1,266	$	—	$	3,265

Change in Projected Benefit Obligation

Benefit Obligations — A comparison of the actuarially computed benefit obligation and plan assets for SPS is presented in the following table:

(Thousands of Dollars)	2013			2012
Change in Projected Benefit Obligation:
Obligation at Jan. 1	$	59,260		$	55,165
Service cost	1,368			1,259
Interest cost	2,352			2,831
Medicare subsidy reimbursements	63			404
Plan amendments	—			(4,334		)
Plan participants’ contributions	698			2,004
Actuarial (gain) loss	(5,215		)	7,120
Benefit payments	(3,544		)	(5,189		)
Obligation at Dec. 31	$	54,982		$	59,260

Change in Fair Value of Plan Assets

(Thousands of Dollars)	2013			2012
Change in Fair Value of Plan Assets:
Fair value of plan assets at Jan. 1	$	46,222		$	39,679
Actual return on plan assets	3,228			5,375
Plan participants’ contributions	698			2,004
Employer contributions	134			4,353
Benefit payments	(3,544		)	(5,189		)
Fair value of plan assets at Dec. 31	$	46,738		$	46,222

Funded Status of Plans

(Thousands of Dollars)	2013			2012
Funded Status of Plans at Dec. 31:
Funded status (a)	$	(8,244	)	$	(13,038	)

^(a)  Amounts are recognized in noncurrent liabilities on SPS’ balance sheet.

Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost

(Thousands of Dollars)	2013			2012
Amounts Not Yet Recognized as Components of Net Periodic Benefit Credit:
Net gain	$	(5,344	)	$	(90	)
Prior service credit	(3,833		)	(4,317		)
Transition obligations	—			—
Total	$	(9,177	)	$	(4,407	)

Amounts Not Yet Recognized as Components of Net Periodic Benefit Costs Recorded on the Balance Sheet Based Upon Expected Recovery in Rates

(Thousands of Dollars)	2013			2012
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates:
Current regulatory liabilities	$	(319	)	$	(954	)
Noncurrent regulatory liabilities	(8,858		)	(3,453		)
Total	$	(9,177	)	$	(4,407	)

Schedule of Assumptions Used

Measurement date Dec. 31, 2013 Dec. 31, 2012

	2013		2012
Significant Assumptions Used to Measure Benefit Obligations:
Discount rate for year-end valuation	4.82	%	4.10	%
Mortality table	RP 2000		RP 2000
Health care costs trend rate — initial	7.00	%	7.50	%

	2013		2012		2011
Significant Assumptions Used to Measure Costs:
Discount rate	4.10	%	5.00	%	5.50	%
Expected average long-term rate of return on assets	7.11		6.75		7.50

Components of Net Periodic Benefit Costs

Benefit Costs — The components of SPS’ net periodic postretirement benefit cost were:

(Thousands of Dollars)	2013			2012			2011
Service cost	$	1,368		$	1,259		$	1,092
Interest cost	2,352			2,831			2,722
Expected return on plan assets	(3,183		)	(2,701		)	(3,006		)
Amortization of transition obligation	—			1,545			1,669
Amortization of prior service credit	(484		)	(148		)	(51		)
Amortization of net (gain) loss	(6		)	1,256			855
Net periodic postretirement benefit cost	$	47		$	4,042		$	3,281

Effects of One-Percent Change in Assumed Health Care Cost Trend Rate

A one-percent change in the assumed health care cost trend rate would have the following effects on SPS:

	One-Percentage Point
(Thousands of Dollars)	Increase		Decrease
APBO	$	5,684	$	(4,763	)
Service and interest components	368		(290		)