Benefit Plans and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2017

Benefit Plans and Other Postretirement Benefits [Abstract]

Projected Benefit Payments for the Pension and Postretirement Benefit Plans

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
2018	$	30,475	$	3,277	$	22	$	3,255
2019	28,755		3,189		19		3,170
2020	29,621		3,229		21		3,208
2021	29,721		3,351		25		3,326
2022	30,712		3,384		30		3,354
2023-2027	155,784		14,773		141		14,632

Pension Plan [Member]

Benefit Plans and Other Postretirement Benefits [Abstract]

Target Asset Allocations and Plan Assets Measured at Fair Value

The following table presents the target pension asset allocations for SPS at Dec. 31 for the upcoming year:

	2017		2016
Domestic and international equity securities	34	%	36	%
Long-duration fixed income and interest rate swap securities	31		31
Short-to-intermediate fixed income securities	19		15
Alternative investments	14		16
Cash	2		2
Total	100	%	100	%

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, 2017 and 2016:

	Dec. 31, 2017
(Thousands of Dollars)	Level 1			Level 2		Level 3		Investments Measured at NAV		Total
Cash equivalents	$	26,934		$	—	$	—	$	—	$	26,934
Commingled funds:
U.S. equity funds	68,103			—		—		—		68,103
Non U.S. equity funds	12,156			—		—		26,427		38,583
U.S. corporate bond funds	54,830			—		—		—		54,830
Emerging market equity funds	—			—		—		41,706		41,706
Emerging market debt funds	9,967			—		—		22,063		32,030
Private equity investments	—			—		—		11,168		11,168
Real estate	—			—		—		25,896		25,896
Other commingled funds	643			—		—		15,476		16,119
Debt securities:
Government securities	—			57,578		—		—		57,578
U.S. corporate bonds	—			41,041		—		—		41,041
Non U.S. corporate bonds	—			6,717		—		—		6,717
Equity securities:
U.S. equities	15,157			—		—		—		15,157
Other	(3,271		)	566		—		72		(2,633		)
Total	$	184,519		$	105,902	$	—	$	142,808	$	433,229

	Dec. 31, 2016
(Thousands of Dollars)	Level 1		Level 2			Level 3		Investments Measured at NAV		Total
Cash equivalents	$	29,237	$	—		$	—	$	—	$	29,237
Commingled funds:
U.S. equity funds	62,899		—			—		—		62,899
Non U.S. equity funds	24,472		—			—		21,931		46,403
U.S. corporate bond funds	41,226		—			—		—		41,226
Emerging market equity funds	—		—			—		24,637		24,637
Emerging market debt funds	9,825		—			—		10,574		20,399
Commodity funds	—		—			—		2,876		2,876
Private equity investments	—		—			—		12,098		12,098
Real estate	—		—			—		23,232		23,232
Other commingled funds	—		—			—		28,247		28,247
Debt securities:
Government securities	—		38,105			—		—		38,105
U.S. corporate bonds	—		36,293			—		—		36,293
Non U.S. corporate bonds	—		5,818			—		—		5,818
Mortgage-backed securities	—		821			—		—		821
Asset-backed securities	—		389			—		—		389
Equity securities:
U.S. equities	10,477		—			—		—		10,477
Other	—		(2,762		)	—		—		(2,762		)
Total	$	178,136	$	78,664		$	—	$	123,595	$	380,395

Change in Projected Benefit Obligation

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

(Thousands of Dollars)	2017			2016
Accumulated Benefit Obligation at Dec. 31	$	478,843		$	453,317
Change in Projected Benefit Obligation:
Obligation at Jan. 1	$	483,601		$	467,394
Service cost	9,758			9,761
Interest cost	19,710			21,259
Plan amendments	(984		)	—
Actuarial loss	31,218			25,053
Transfer to other plan	—			(3,305		)
Benefit payments	(27,424		)	(36,561		)
Obligation at Dec. 31	$	515,879		$	483,601

Change in Fair Value of Plan Assets

(Thousands of Dollars)	2017			2016
Change in Fair Value of Plan Assets:
Fair value of plan assets at Jan. 1	$	380,395		$	378,913
Actual return on plan assets	56,756			23,306
Employer contributions	23,502			18,088
Transfer to other plan	—			(3,351		)
Benefit payments	(27,424		)	(36,561		)
Fair value of plan assets at Dec. 31	$	433,229		$	380,395

Funded Status of Plans

(Thousands of Dollars)	2017			2016
Funded Status of Plans at Dec. 31:
Funded status (a)	$	(82,650	)	$	(103,206	)

^(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)	2017			2016
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost:
Net loss	$	237,024		$	247,381
Prior service credit	(1,372		)	—
Total	$	235,652		$	247,381

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)	2017		2016
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	$	13,851	$	13,524
Noncurrent regulatory assets	221,801		233,857
Total	$	235,652	$	247,381

Schedule of Assumptions Used

Measurement date Dec. 31, 2017 Dec. 31, 2016

	2017		2016
Significant Assumptions Used to Measure Benefit Obligations:
Discount rate for year-end valuation	3.63	%	4.13	%
Expected average long-term increase in compensation level	3.75		3.75
Mortality table	RP-2014		RP-2014

	2017		2016		2015
Significant Assumptions Used to Measure Costs:
Discount rate	4.13	%	4.66	%	4.11	%
Expected average long-term increase in compensation level	3.75		4.00		3.75
Expected average long-term rate of return on assets	6.78		6.78		7.22

Components of Net Periodic Benefit Costs

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

(Thousands of Dollars)	2017			2016			2015
Service cost	$	9,758		$	9,761		$	11,006
Interest cost	19,710			21,259			20,184
Expected return on plan assets	(27,883		)	(27,602		)	(28,610		)
Amortization of prior service cost	—			—			39
Amortization of net loss	12,981			11,986			15,087
Net periodic pension cost	14,566			15,404			17,706
Credits not recognized due to effects of regulation	306			2,042			2,597
Net benefit cost recognized for financial reporting	$	14,872		$	17,446		$	20,303

Other Postretirement Benefits Plan [Member]

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’ proportionate allocation of the total postretirement benefit plan assets that are measured at fair value as of Dec. 31, 2017 and 2016:

	Dec. 31, 2017
(Thousands of Dollars)	Level 1		Level 2		Level 3		Investments Measured at NAV		Total
Cash equivalents	$	2,787	$	—	$	—	$	—	$	2,787
Insurance contracts	—		4,716		—		—		4,716
Commingled funds:
U.S. equity funds	7,032		—		—		—		7,032
U.S fixed income funds	3,245		—		—		—		3,245
Emerging market debt funds	3,836		—		—		—		3,836
Debt securities:
Government securities	—		5,480		—		—		5,480
U.S. corporate bonds	—		5,995		—		—		5,995
Non U.S. corporate bonds	—		2,027		—		—		2,027
Asset-backed securities	—		2,218		—		—		2,218
Mortgage-backed securities	—		3,276		—		—		3,276
Equity securities:
Non U.S. equities	3,323		—		—		—		3,323
Other	—		104		—		—		104
Total	$	20,223	$	23,816	$	—	$	—	$	44,039

	Dec. 31, 2016
(Thousands of Dollars)	Level 1		Level 2		Level 3		Investments Measured at NAV		Total
Cash equivalents	$	1,966	$	—	$	—	$	—	$	1,966
Insurance contracts	—		4,519		—		—		4,519
Commingled funds:
U.S. equity funds	5,208		—		—		—		5,208
U.S fixed income funds	2,593		—		—		—		2,593
Emerging market debt funds	2,911		—		—		—		2,911
Other commingled funds	—		—		—		5,258		5,258
Debt securities:
Government securities	—		3,611		—		—		3,611
U.S. corporate bonds	—		5,962		—		—		5,962
Non U.S. corporate bonds	—		1,653		—		—		1,653
Asset-backed securities	—		1,810		—		—		1,810
Mortgage-backed securities	—		2,748		—		—		2,748
Equity securities:
Non U.S. equities	3,919		—		—		—		3,919
Other	—		139		—		—		139
Total	$	16,597	$	20,442	$	—	$	5,258	$	42,297

The following table presents the target postretirement asset allocations for Xcel Energy Inc. and SPS at Dec. 31 for the upcoming year:

	2017		2016
Domestic and international equity securities	24	%	25	%
Short-to-intermediate fixed income securities	60		57
Alternative investments	9		13
Cash	7		5
Total	100	%	100	%

Change in Projected Benefit Obligation

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

(Thousands of Dollars)	2017			2016
Change in Projected Benefit Obligation:
Obligation at Jan. 1	$	41,860		$	40,864
Service cost	875			775
Interest cost	1,659			1,821
Medicare subsidy reimbursements	14			31
Plan participants’ contributions	637			653
Actuarial loss	4,688			1,293
Benefit payments	(2,764		)	(3,577		)
Obligation at Dec. 31	$	46,969		$	41,860

Change in Fair Value of Plan Assets

(Thousands of Dollars)	2017			2016
Change in Fair Value of Plan Assets:
Fair value of plan assets at Jan. 1	$	42,297		$	42,684
Actual return on plan assets	3,686			1,978
Plan participants’ contributions	637			653
Employer contributions	183			559
Benefit payments	(2,764		)	(3,577		)
Fair value of plan assets at Dec. 31	$	44,039		$	42,297

Funded Status of Plans

(Thousands of Dollars)	2017			2016
Funded Status of Plans at Dec. 31:
Funded status (a)	$	(2,930	)	$	437

^(a)  Amounts are recognized in noncurrent liabilities and noncurrent assets on SPS’ balance sheet as of Dec. 31, 2017 and 2016, respectively.

Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost

(Thousands of Dollars)	2017			2016
Amounts Not Yet Recognized as Components of Net Periodic Benefit Credit:
Net gain	$	(8,620	)	$	(12,595	)
Prior service credit	(2,229		)	(2,630		)
Total	$	(10,849	)	$	(15,225	)

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)	2017			2016
Amounts Not Yet Recognized as Components of Net Periodic Benefit Credit Have Been Recorded as Follows Based Upon Expected Recovery in Rates:
Current regulatory liabilities	$	(827	)	$	(1,004	)
Noncurrent regulatory liabilities	(10,022		)	(14,221		)
Total	$	(10,849	)	$	(15,225	)

Schedule of Assumptions Used

	2017		2016		2015
Significant Assumptions Used to Measure Costs:
Discount rate	4.13	%	4.65	%	4.08	%
Expected average long-term rate of return on assets	5.80		5.80		5.80

Measurement date Dec. 31, 2017 Dec. 31, 2016

	2017		2016
Significant Assumptions Used to Measure Benefit Obligations:
Discount rate for year-end valuation	3.62	%	4.13	%
Mortality table	RP 2014		RP 2014
Health care costs trend rate — initial Pre-65	7.00	%	5.50	%
Health care costs trend rate — initial Post-65	5.50	%	5.50	%

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	$	4,559	$	(3,858	)
Service and interest components	266		(225		)

Components of Net Periodic Benefit Costs

The components of SPS’ net periodic postretirement benefit costs were:

(Thousands of Dollars)	2017			2016			2015
Service cost	$	875		$	775		$	954
Interest cost	1,659			1,821			1,745
Expected return on plan assets	(2,355		)	(2,377		)	(2,540		)
Amortization of prior service credit	(401		)	(401		)	(401		)
Amortization of net gain	(618		)	(583		)	(639		)
Net periodic postretirement benefit credit	$	(840	)	$	(765	)	$	(881	)