Benefit Plans and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2017

Benefit Plans and Other Postretirement Benefits [Abstract]

Change in Projected Benefit Obligation

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

(Thousands of Dollars)	2017			2016
Accumulated Benefit Obligation at Dec. 31	$	145,387		$	146,448
Change in Projected Benefit Obligation:
Obligation at Jan. 1	$	157,457		$	152,545
Service cost	4,618			4,417
Interest cost	6,218			6,816
Plan amendments	(713		)	305
Actuarial loss	6,499			7,315
Benefit payments (a)	(17,331		)	(13,941		)
Obligation at Dec. 31	$	156,748		$	157,457

Projected Benefit Payments for the Pension and Postretirement Benefit Plans

The following table lists NSP-Wisconsin’s projected benefit payments for the pension and postretirement benefit plans:

(Thousands of Dollars)	ProjectedPension BenefitPayments		Gross Projected Postretirement Health Care BenefitPayments		ExpectedMedicare Part DSubsidies		Net Projected Postretirement Health Care BenefitPayments
2018	$	11,189	$	1,352	$	5	$	1,347
2019	11,812		1,329		4		1,325
2020	12,361		1,298		3		1,295
2021	11,842		1,254		3		1,251
2022	11,640		1,215		3		1,212
2023-2027	58,627		5,111		14		5,097

Contributions to Multiemployer Plans

Contributions to multiemployer plans were as follows for the years ended Dec. 31, 2017, 2016 and 2015. There were no significant changes to the nature or magnitude of the participation of NSP-Wisconsin in multiemployer plans for the years presented:

(Thousands of Dollars)	2017		2016		2015
Multiemployer plan contributions:
Pension	$	248	$	707	$	944

Pension 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, NSP-Wisconsin’s 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	$	8,091		$	—	$	—	$	—	$	8,091
Commingled funds:
U.S. equity funds	21,850			—		—		—		21,850
Non U.S. equity funds	3,900			—		—		8,479		12,379
U.S. corporate bond funds	14,035			—		—		—		14,035
Emerging market equity funds	—			—		—		13,381		13,381
Emerging market debt funds	3,198			—		—		7,079		10,277
Private equity investments	—			—		—		3,583		3,583
Real estate	—			—		—		8,309		8,309
Other commingled funds	206			—		—		4,965		5,171
Debt securities:
Government securities	—			12,167		—		—		12,167
U.S. corporate bonds	—			10,178		—		—		10,178
Non U.S. corporate bonds	—			1,730		—		—		1,730
Equity securities:
U.S. equities	4,863			—		—		—		4,863
Other	(1,334		)	149		—		23		(1,162		)
Total	$	54,809		$	24,224	$	—	$	45,819	$	124,852

	Dec. 31, 2016
(Thousands of Dollars)	Level 1		Level 2		Level 3		Investments Measured at NAV		Total
Cash equivalents	$	3,939	$	—	$	—	$	—	$	3,939
Commingled funds:
U.S. equity funds	21,415		—		—		—		21,415
Non U.S. equity funds	7,406		—		—		8,942		16,348
U.S. corporate bond funds	10,581		—		—		—		10,581
Emerging market equity funds	—		—		—		8,577		8,577
Emerging market debt funds	3,519		—		—		3,787		7,306
Commodity funds	—		—		—		889		889
Private equity investments	—		—		—		4,652		4,652
Real estate	—		—		—		8,108		8,108
Other commingled funds	—		—		—		8,752		8,752
Debt securities:
Government securities	—		12,773		—		—		12,773
U.S. corporate bonds	—		9,432		—		—		9,432
Non U.S. corporate bonds	—		1,514		—		—		1,514
Mortgage-backed securities	—		254		—		—		254
Asset-backed securities	—		120		—		—		120
Equity securities:
U.S. equities	4,219		—		—		—		4,219
Other	—		97		—		—		97
Total	$	51,079	$	24,190	$	—	$	43,707	$	118,976

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

	2017		2016
Domestic and international equity securities	38	%	40	%
Long-duration fixed income and interest rate swap securities	23		23
Short-to-intermediate fixed income securities	21		16
Alternative investments	16		19
Cash	2		2
Total	100	%	100	%

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	$	118,976		$	119,314
Actual return on plan assets	13,923			6,163
Employer contributions	9,284			7,440
Benefit payments (a)	(17,331		)	(13,941		)
Fair value of plan assets at Dec. 31	$	124,852		$	118,976

Funded Status of Plans

(Thousands of Dollars)	2017			2016
Funded Status of Plans at Dec. 31:
Funded status (b)	$	(31,896	)	$	(38,481	)

^(a)  2017 amount includes approximately $13 million of lump-sum benefit payments used in the determination of a settlement charge.

^(b)  Amounts are recognized in noncurrent liabilities on NSP-Wisconsin’s consolidated 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	$	80,429		$	91,531
Prior service (credit) cost	(346		)	750
Total	$	80,083		$	92,281

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	$	5,548	$	5,972
Noncurrent regulatory assets	74,535		86,309
Total	$	80,083	$	92,281

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	7.10		7.10		7.25

Components of Net Periodic Benefit Costs

The components of NSP-Wisconsin’s net periodic pension cost were:

(Thousands of Dollars)	2017			2016			2015
Service cost	$	4,618		$	4,417		$	4,759
Interest cost	6,218			6,816			6,520
Expected return on plan assets	(9,180		)	(9,157		)	(9,483		)
Amortization of prior service cost	138			111			111
Amortization of net loss	5,846			5,392			6,804
Settlement charge (a)	7,107			—			—
Net periodic pension cost	14,747			7,579			8,711
Costs not recognized due to effects of regulation	(4,176		)	—			—
Net benefit cost recognized for financial reporting	$	10,571		$	7,579		$	8,711

^(a)  A settlement charge is required when the amount of lump-sum distributions during the year is greater than the sum of the service and interest cost components of the annual net periodic pension cost. In the fourth quarter of 2017 as a result of lump-sum distributions during the 2017 plan year, NSP-Wisconsin recorded a total pension settlement charge of $7 million, the majority of which was not recognized due to the effects of regulation. A total of $2 million of that amount was recorded in O&M expenses in the fourth quarter of 2017.

	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	7.10		7.10		7.25

Other Postretirement Benefits 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 postretirement asset allocations for Xcel Energy Inc. and NSP-Wisconsin 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	%

The following tables present, for each of the fair value hierarchy levels, NSP-Wisconsin’s 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	$	68	$	—	$	—	$	—	$	68
Insurance contracts	—		115		—		—		115
Commingled funds:
U.S. equity funds	172		—		—		—		172
U.S fixed income funds	79		—		—		—		79
Emerging market debt funds	94		—		—		—		94
Debt securities:
Government securities	—		134		—		—		134
U.S. corporate bonds	—		147		—		—		147
Non U.S. corporate bonds	—		50		—		—		50
Asset-backed securities	—		54		—		—		54
Mortgage-backed securities	—		80		—		—		80
Equity securities:
Non U.S. equities	82		—		—		—		82
Other	—		3		—		—		3
Total	$	495	$	583	$	—	$	—	$	1,078

	Dec. 31, 2016
(Thousands of Dollars)	Level 1		Level 2		Level 3		Investments Measured at NAV		Total
Cash equivalents	$	25	$	—	$	—	$	—	$	25
Insurance contracts	—		58		—		—		58
Commingled funds:
U.S. equity funds	67		—		—		—		67
U.S fixed income funds	33		—		—		—		33
Emerging market debt funds	38		—		—		—		38
Other commingled funds	—		—		—		67		67
Debt securities:
Government securities	—		46		—		—		46
U.S. corporate bonds	—		77		—		—		77
Non U.S. corporate bonds	—		21		—		—		21
Asset-backed securities	—		23		—		—		23
Mortgage-backed securities	—		36		—		—		36
Equity securities:
Non U.S. equities	50		—		—		—		50
Other	—		2		—		—		2
Total	$	213	$	263	$	—	$	67	$	543

Change in Projected Benefit Obligation

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

(Thousands of Dollars)	2017			2016
Change in Projected Benefit Obligation:
Obligation at Jan. 1	$	14,973		$	14,718
Service cost	29			24
Interest cost	590			651
Medicare subsidy reimbursements	—			7
Plan participants’ contributions	71			87
Actuarial loss	2,069			775
Benefit payments	(1,368		)	(1,289		)
Obligation at Dec. 31	$	16,364		$	14,973

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	$	543		$	418
Actual loss on plan assets	(6		)	(12		)
Plan participants’ contributions	71			87
Employer contributions	1,838			1,339
Benefit payments	(1,368		)	(1,289		)
Fair value of plan assets at Dec. 31	$	1,078		$	543

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	$	10,553		$	8,883
Prior service credit	(1,783		)	(2,134		)
Total	$	8,770		$	6,749

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	$	110	$	—
Noncurrent regulatory assets	8,660		6,749
Total	$	8,770	$	6,749

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	3.62	%	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	%

	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

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 NSP-Wisconsin:

	One-Percentage Point
(Thousands of Dollars)	Increase		Decrease
APBO	$	1,588	$	(1,344	)
Service and interest components	65		(55		)

Components of Net Periodic Benefit Costs

The components of NSP-Wisconsin’s net periodic postretirement benefit costs were:

(Thousands of Dollars)	2017			2016			2015
Service cost	$	29		$	24		$	29
Interest cost	590			651			653
Expected return on plan assets	(31		)	(24		)	(30		)
Amortization of prior service credit	(351		)	(351		)	(351		)
Amortization of net loss	436			330			456
Net periodic postretirement benefit cost	$	673		$	630		$	757