Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	Apr. 26, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	SOUTHWESTERN PUBLIC SERVICE CO
Entity Central Index Key	0000092521
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Entity Emerging Growth Company	false
Entity Small Business	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		100

CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Common Stock	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Common Stock, Dividends, Per Share, Declared	$ 0
Beginning balance at Dec. 31, 2017	$ 2,130.3	$ 0.0	$ 1,590.2	$ 541.6	$ (1.5)
Balance (in shares) at Dec. 31, 2017		100
Increase (Decrease) in Stockholders' Equity
Net income	33.1			33.1
Other comprehensive income	0.1				0.1
Dividends declared on common stock	(33.3)			(33.3)
Ending balance at Mar. 31, 2018	$ 2,130.2	$ 0.0	1,590.2	541.4	(1.4)
Balance (in shares) at Mar. 31, 2018		100
Common Stock, Dividends, Per Share, Declared	$ 0
Beginning balance at Dec. 31, 2018	$ 2,536.6	$ 0.0	1,932.3	605.7	(1.4)
Balance (in shares) at Dec. 31, 2018	100	100
Increase (Decrease) in Stockholders' Equity
Net income	$ 54.1			54.1
Other comprehensive income	0.0
Dividends declared on common stock	(57.5)			(57.5)
Ending balance at Mar. 31, 2019	$ 2,533.2	$ 0.0	$ 1,932.3	$ 602.3	$ (1.4)
Balance (in shares) at Mar. 31, 2019	100	100

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Revenues [Abstract]
Operating revenues	$ 454.1	$ 447.2
Operating expenses
Electric fuel and purchased power	230.9	253.9
Operating and maintenance expenses	72.4	66.1
Demand side management expenses	4.6	4.1
Depreciation and amortization	53.2	48.4
Taxes (other than income taxes)	18.5	17.6
Total operating expenses	379.6	390.1
Operating income	74.5	57.1
Other income (expense), net	(0.4)	(0.7)
Allowance for funds used during construction — equity	10.3	3.4
Interest charges and financing costs
Interest charges — includes other financing costs of $0.8 and $0.7 respectively	24.4	20.2
Allowance for funds used during construction — debt	(4.5)	(1.8)
Total interest charges and financing costs	19.9	18.4
Income before income taxes	65.3	41.4
Income taxes	11.2	8.3
Net income	$ 54.1	$ 33.1

STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Interest charges and financing costs
Other financing costs	$ 0.8	$ 0.7

STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Comprehensive income:
Net income	$ 54.1	$ 33.1
Derivative instruments:
Reclassification of losses to net income, net of tax of $0 and $0, respectively	0.0	0.1
Other comprehensive income	0.0	0.1
Comprehensive income	$ 54.1	$ 33.2

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative instruments:
Reclassification of losses to net income, tax	$ 0	$ 0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax	$ 0	$ 0

STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities
Net income	$ 54.1	$ 33.1
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	53.8	48.5
Demand side management program amortization	0.0	0.4
Deferred income taxes	11.0	0.8
Allowance for equity funds used during construction	(10.3)	(3.4)
Other, net	0.3	0.2
Changes in operating assets and liabilities:
Accounts receivable	(1.3)	(11.4)
Accrued unbilled revenues	0.2	12.1
Inventories	(6.8)	6.0
Prepayments and other	(5.4)	1.4
Accounts payable	(9.3)	(12.0)
Net regulatory assets and liabilities	(1.2)	27.0
Other current liabilities	(16.7)	(4.9)
Pension and other employee benefit obligations	(15.9)	(7.9)
Net cash provided by operating activities	52.5	89.9
Investing activities
Utility capital/construction expenditures	(179.6)	(145.5)
Allowance for equity funds used during construction	10.3	3.4
Investments in utility money pool arrangement	0.0	46.0
Repayments from utility money pool arrangement	0.0	111.0
Net cash used in investing activities	(179.6)	(80.5)
Financing activities
Proceeds from short-term borrowings, net	95.0	10.0
Borrowings under utility money pool arrangement	100.0	1.0
Repayments under utility money pool arrangement	(62.0)	(1.0)
Capital contributions from parent	5.8	0.4
Repayment of long-term debt	(0.1)	0.0
Dividends paid to parent	(55.1)	(26.8)
Net cash provided by (used in) financing activities	83.6	(16.4)
Net change in cash and cash equivalents	(43.5)	(7.0)
Cash and cash equivalents at beginning of period	44.0	10.9
Cash and cash equivalents at end of period	0.5	3.9
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(18.9)	(21.2)
Cash paid for income taxes, net	(4.9)	(4.0)
Supplemental disclosure of non-cash investing and financing transactions:
Property, plant and equipment additions in accounts payable	68.5	36.7
Inventory transfers to plant, property and equipment	6.4	4.8
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 548.3	$ 0.0

BALANCE SHEETS (UNAUDITED) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 0.5	$ 44.0
Accounts receivable, net	93.2	90.7
Accounts receivable from affiliates	3.4	10.5
Accrued unbilled revenues	114.3	114.5
Public Utilities, Inventory	34.3	33.9
Regulatory assets	25.4	26.0
Derivative instruments	6.2	17.8
Property, Plant and Equipment, Gross	8,261.5	8,075.0
Prepaid taxes	14.2	14.2
Prepayments and other	16.1	10.7
Total current assets	307.6	362.3
Property, Plant and Equipment, Net	6,088.5	5,946.4
Other assets
Regulatory assets	364.6	366.2
Derivative instruments	15.0	15.8
Operating Lease, Right-of-Use Asset	542.0	0.0
Other	5.0	5.1
Total other assets	926.6	387.1
Total assets	7,322.7	6,695.8
Current liabilities
Short-term debt	137.0	42.0
Borrowings Payable Under Utility Money Pool Arrangement	38.0	0.0
Accounts payable	194.4	191.8
Accounts payable to affiliates	13.1	19.9
Regulatory liabilities	84.7	85.8
Taxes accrued	28.8	41.6
Accrued interest	26.1	25.8
Dividends payable	47.6	45.2
Derivative instruments	3.6	3.6
Other	49.4	28.3
Total current liabilities	622.7	484.0
Deferred credits and other liabilities
Deferred income taxes	635.4	619.1
Regulatory liabilities	756.6	780.9
Asset retirement obligations	32.8	32.4
Derivative instruments	15.5	16.4
Pension and employee benefit obligations	76.4	92.4
Noncurrent operating lease liabilities	515.8	0.0
Other	8.0	7.9
Total deferred credits and other liabilities	2,040.5	1,549.1
Capitalization
Long-term debt	2,126.3	2,126.1
Common stock — 200 shares authorized of $1.00 par value; 100 shares outstanding at March 31, 2019 and Dec. 31, 2018, respectively	0.0	0.0
Additional paid in capital	1,932.3	1,932.3
Retained earnings	602.3	605.7
Accumulated other comprehensive loss	(1.4)	(1.4)
Total common stockholder’s equity	2,533.2	2,536.6
Total liabilities and equity	$ 7,322.7	$ 6,695.8

BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Capitalization, Long-term Debt and Equity [Abstract]
Common stock, shares authorized (in shares)	200	200
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, shares outstanding (in shares)	100	100

Management's Opinion	3 Months Ended
Management's Opinion	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Management's Opinion	In the opinion of management, the accompanying unaudited financial statements contain all adjustments necessary to present fairly, in accordance with accounting principles generally accepted in the United States of America (GAAP), the financial position of SPS as of March 31, 2019 and Dec. 31, 2018; the results of its operations, including the components of net income and comprehensive income, and change in stockholder’s equity for the three months ended March 31, 2019 and 2018; and its cash flows for the three months ended March 31, 2019 and 2018. All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after March 31, 2019 up to the date of issuance of these financial statements. These statements contain all necessary adjustments and disclosures resulting from that evaluation. The Dec. 31, 2018 balance sheet information has been derived from the audited 2018 financial statements included in the SPS Annual Report on Form 10-K for the year ended Dec. 31, 2018. These notes to the financial statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP on an annual basis have been condensed or omitted pursuant to such rules and regulations. For further information, refer to the financial statements and notes thereto, included in the SPS Annual Report on Form 10-K for the year ended Dec. 31, 2018, filed with the SEC on Feb. 22, 2019. Due to the seasonality of SPS’ electric sales, interim results are not necessarily an appropriate base from which to project annual results.

Summary of Significant Accounting Policies	3 Months Ended
Summary of Significant Accounting Policies	Mar. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The significant accounting policies set forth in Note 1 to the financial statements in the SPS Annual Report on Form 10-K for the year ended Dec. 31, 2018, appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.

Accounting Pronouncements	3 Months Ended
Accounting Pronouncements	Mar. 31, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Accounting Pronouncements	Accounting Pronouncements Recently Issued Credit Losses — In 2016, the FASB issued Financial Instruments - Credit Losses, Topic 326 (ASC Topic 326), which changes how entities account for credit losses on receivables and certain other assets. The guidance requires use of a current expected loss model, which may result in earlier recognition of credit losses than under previous accounting standards. ASC Topic 326 is effective for interim and annual periods beginning on or after Dec. 15, 2019. SPS is currently evaluating the impact of adoption of the new standard on its financial statements. Recently Adopted Leases — In 2016, the FASB issued Leases, Topic 842 (ASC Topic 842), which provides new accounting and disclosure guidance for leasing activities, most significantly requiring that operating leases be recognized on the balance sheet. SPS adopted the guidance on Jan. 1, 2019 utilizing the package of transition practical expedients provided by the new standard, including carrying forward prior conclusions on whether agreements existing before the adoption date contain leases and whether existing leases are operating or finance leases; ASC Topic 842 refers to capital leases as finance leases. Specifically for land easement contracts, SPS has elected the practical expedient provided by ASU No. 2018-01 Leases: Land Easement Practical Expedient for Transition to Topic 842, and as a result, only those easement contracts entered on or after Jan. 1, 2019 will be evaluated to determine if lease treatment is appropriate. SPS also utilized the transition practical expedient offered by ASU No. 2018-11 Leases: Targeted Improvements to implement the standard on a prospective basis. As a result, reporting periods in the financial statements beginning Jan. 1, 2019 reflect the implementation of ASC Topic 842, while prior periods continue to be reported in accordance with Leases, Topic 840 (ASC Topic 840). Other than first-time recognition of operating leases on its balance sheet, the implementation of ASC Topic 842 did not have a significant impact on SPS’ financial statements. Adoption resulted in recognition of approximately $0.5 billion of operating lease ROU assets and current/noncurrent operating lease liabilities. See Note 9 for leasing disclosures.

Selected Balance Sheet Data

3 Months Ended

Mar. 31, 2019

Balance Sheet Related Disclosures [Abstract]

Selected Balance Sheet Data



(Millions of Dollars)	March 31, 2019			Dec. 31, 2018
Accounts receivable, net
Accounts receivable	$	98.7		$	96.3
Less allowance for bad debts	(5.5		)	(5.6		)
	$	93.2		$	90.7



(Millions of Dollars)	March 31, 2019		Dec. 31, 2018
Inventories
Materials and supplies	$	25.8	$	25.7
Fuel	8.5		8.2
	$	34.3	$	33.9



(Millions of Dollars)	March 31, 2019			Dec. 31, 2018
Property, plant and equipment, net
Electric plant	$	7,287.2		$	7,227.7
Construction work in progress	974.3			847.3
Total property, plant and equipment	8,261.5			8,075.0
Less accumulated depreciation	(2,173.0		)	(2,128.6		)
Total	$	6,088.5		$	5,946.4

Borrowings and Other Financing Instruments

3 Months Ended

Mar. 31, 2019

Debt Disclosure [Abstract]

Borrowings and Other Financing Instruments

Short-Term Borrowings

SPS meets its short-term liquidity requirements primarily through the issuance of commercial paper and borrowings under its credit facility and the money pool.

Money Pool — Xcel Energy Inc. and its utility subsidiaries have established a money pool arrangement that allows for short-term investments in and borrowings between the utility subsidiaries. Xcel Energy Inc. may make investments in the utility subsidiaries at market-based interest rates; however, the money pool arrangement does not allow the utility subsidiaries to make investments in Xcel Energy Inc. Money pool borrowings for SPS were as follows:



(Amounts in Millions, Except Interest Rates)	Three Months Ended March 31, 2019			Year Ended Dec. 31, 2018
Borrowing limit	$	100		$	100
Amount outstanding at period end	38			—
Average amount outstanding	19			29
Maximum amount outstanding	100			100
Weighted average interest rate, computed on a daily basis	2.44		%	1.96		%
Weighted average interest rate at period end	2.44			N/A

Commercial Paper — Commercial paper outstanding for SPS was as follows:



(Amounts in Millions, Except Interest Rates)	Three Months Ended March 31, 2019			Year Ended Dec. 31, 2018
Borrowing limit	$	400		$	400
Amount outstanding at period end	137			42
Average amount outstanding	86			30
Maximum amount outstanding	152			144
Weighted average interest rate, computed on a daily basis	2.69		%	2.27		%
Weighted average interest rate at period end	2.71			2.80

Letters of Credit — SPS uses letters of credit, generally with terms of one year, to provide financial guarantees for certain operating obligations. As of both March 31, 2019 and Dec. 31, 2018, there were $2 million of letters of credit outstanding under the credit facility. The contract amounts of these letters of credit approximate their fair value and are subject to fees.

Credit Facility — In order to use its commercial paper program to fulfill short-term funding needs, SPS must have a revolving credit facility in place at least equal to the amount of its commercial paper borrowing limit and cannot issue commercial paper in an aggregate amount exceeding available capacity under this credit facility. The line of credit provides short-term financing in the form of notes payable to banks, letters of credit and back-up support for commercial paper borrowings.

As of March 31, 2019, SPS had the following committed credit facility available (in millions of dollars):



Credit Facility ^(a)		Outstanding ^(b)		Available
$	400	$	139	$	261


^(a)	This credit facility expires in June 2021.


^(b)	Includes outstanding commercial paper and letters of credit.

All credit facility bank borrowings, outstanding letters of credit and outstanding commercial paper reduce the available capacity under the credit facility. SPS had no direct advances on the credit facility outstanding as of March 31, 2019 and Dec. 31, 2018.

Revenues

3 Months Ended

Mar. 31, 2019

Revenue from Contract with Customer [Abstract]

Revenue

Revenues

Revenue is classified by the type of goods/services rendered and market/customer type. SPS’ operating revenues consists of the following:



	Three Months Ended
(Millions of Dollars)	March 31, 2019		March 31, 2018
Major revenue types
Revenue from contracts with customers:
Residential	$	88.1	$	80.0
C&I	205.8		195.8
Other	9.6		9.7
Total retail	303.5		285.5
Wholesale	84.8		93.2
Transmission	57.4		55.7
Other	1.0		7.5
Total revenue from contracts with customers	446.7		441.9
Alternative revenue and other	7.4		5.3
Total revenues	$	454.1	$	447.2

Income Taxes

3 Months Ended

Mar. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

Except to the extent noted below, Note 7 to the consolidated financial statements included in SPS’ Annual Report on Form 10-K for the year ended Dec. 31, 2018 appropriately represents, in all material respects, the current status of other income tax matters, and are incorporated herein by reference.

Total income tax expense from operations differs from the amount computed by applying the statutory federal income tax rate to income before income tax expense. The following reconciles such differences:



	Three Months Ended March 31,
	2019		2018
Federal statutory rate	21.0	%	21.0	%
State tax (net of federal tax effect)	2.1		2.4
Increases (decreases) in tax from:
Regulatory differences ^(a)	(4.6	)	(2.7	)
Tax credits (net)	(0.6	)	(0.7	)
Other (net)	(0.7	)	—
Effective income tax rate	17.2	%	20.0	%

^(a)

Regulatory differences for income tax purposes primarily include the average rate assumption method (ARAM), ARAM deferral and AFUDC - Equity. ARAM is a method to flow back excess deferred taxes to customers. ARAM has been deferred when regulatory treatment has not been established. As Xcel Energy received direction from its regulatory commissions regarding the return of excess deferred taxes to customers, the ARAM deferral was reversed. This resulted in a reduction to tax expense with a corresponding reduction to revenue.

Federal Audits — SPS is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. Statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows:



Tax Year(s)		Expiration
2009 - 2013		October 2019
2014 - 2016		September 2020
2017		September 2021

In the third quarter of 2015, the IRS commenced an examination of tax years 2012 and 2013. In the third quarter of 2017, the IRS concluded the audit of tax years 2012 and 2013 and proposed an adjustment that would impact Xcel Energy’s NOL and ETR. Xcel Energy filed a protest with the IRS. As of March 31, 2019, the case has been forwarded to the Office of Appeals and Xcel Energy has recognized its best estimate of income tax expense that will result from a final resolution of this issue; however, the outcome and timing of a resolution is unknown.

In the fourth quarter of 2018, the IRS began an audit of tax years 2014 - 2016. As of March 31, 2019 no adjustments have been proposed.

State Audits — SPS is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of March 31, 2019, SPS’ earliest open tax year that is subject to examination by state taxing authorities under applicable statutes of limitations is 2009. There are currently no state income tax audits in progress.

Unrecognized Benefits — Unrecognized tax benefit balance includes permanent tax positions, which if recognized would affect the annual ETR. In addition, the unrecognized tax benefit balance includes temporary tax positions for which the ultimate deductibility is highly certain, but for which there is uncertainty about the timing of such deductibility. A change in the period of deductibility would not affect the ETR but would accelerate the payment to the taxing authority to an earlier period.

Unrecognized tax benefits - permanent vs temporary:



(Millions of Dollars)	March 31, 2019		Dec. 31, 2018
Unrecognized tax benefit — Permanent tax positions	$	3.1	$	3.0
Unrecognized tax benefit — Temporary tax positions	1.6		1.5
Total unrecognized tax benefit	$	4.7	$	4.5

Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards:



(Millions of Dollars)	March 31, 2019			Dec. 31, 2018
NOL and tax credit carryforwards	$	(4.0	)	$	(3.8	)

Net deferred tax liability associated with the unrecognized tax benefit amounts and related NOLs and tax credits carryforwards were $0.9 million and $0.8 million at March 31, 2019 and Dec. 31, 2018, respectively.

As the IRS Appeals and federal audit progress and state audits resume, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $3.6 million in the next 12 months.

Payable for interest related to unrecognized tax benefits is partially offset by the interest benefit associated with NOL and tax credit carryforwards.

Interest payable related to unrecognized tax benefits:



(Millions of Dollars)	March 31, 2019		Dec. 31, 2018
Receivable for interest related to unrecognized tax benefits at beginning of period	$	0.7	$	0.5
Interest income related to unrecognized tax benefits	—		0.2
Receivable for interest related to unrecognized tax benefits at end of period	$	0.7	$	0.7

No amounts were accrued for penalties related to unrecognized tax benefits as of March 31, 2019 or Dec. 31, 2018.

Fair Value of Financial Assets and Liabilities

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets and Liabilities

Fair Value Measurements

The accounting guidance for fair value measurements and disclosures provides a single definition of fair value and requires disclosures about assets and liabilities measured at fair value. A hierarchical framework for disclosing the observability of the inputs utilized in measuring assets and liabilities at fair value is established by this guidance.

Level 1 — Quoted prices are available in active markets for identical assets or liabilities as of the reporting date. The types of assets and liabilities included in Level 1 are highly liquid and actively traded instruments with quoted prices.

Level 2 — Pricing inputs are other than quoted prices in active markets, but are either directly or indirectly observable as of the reporting date. The types of assets and liabilities included in Level 2 are typically either comparable to actively traded securities or contracts, or priced with models using highly observable inputs.

Level 3 — Significant inputs to pricing have little or no observability as of the reporting date. The types of assets and liabilities included in Level 3 are those valued with models requiring significant management judgment or estimation.

Specific valuation methods include:

Cash equivalents — The fair values of cash equivalents are generally based on cost plus accrued interest; money market funds are measured using quoted NAVs.

Interest rate derivatives — The fair values of interest rate derivatives are based on broker quotes that utilize current market interest rate forecasts.

Commodity derivatives — The methods used to measure the fair value of commodity derivative forwards and options generally utilize observable forward prices and volatilities, as well as observable pricing adjustments for specific delivery locations, and are generally assigned a Level 2 classification. When contractual settlements relate to delivery locations for which pricing is relatively unobservable, or extend to periods beyond those readily observable on active exchanges or quoted by brokers, the significance of the use of less observable inputs on a valuation is evaluated, and may result in Level 3 classification.

Electric commodity derivatives held by SPS include transmission congestion instruments, generally referred to as FTRs, purchased from SPP. FTRs purchased from an RTO are financial instruments that entitle or obligate the holder to monthly revenues or charges based on transmission congestion across a given transmission path. The value of an FTR is derived from, and designed to offset, the cost of transmission congestion. In addition to overall transmission load, congestion is also influenced by the operating schedules of power plants and the consumption of electricity pertinent to a given transmission path. Unplanned plant outages, scheduled plant maintenance, changes in the relative costs of fuels used in generation, weather and overall changes in demand for electricity can each impact the operating schedules of the power plants on the transmission grid and the value of an FTR.

If forecasted costs of electric transmission congestion increase or decrease for a given FTR path, the value of that particular FTR instrument will likewise increase or decrease. Given the limited observability of important inputs to the value of FTRs between auction processes, including expected plant operating schedules and retail and wholesale demand, fair value measurements for FTRs have been assigned a Level 3. Non-trading monthly FTR settlements are expected to be recovered through fuel and purchased energy cost recovery mechanisms, and therefore changes in the fair value of the yet to be settled portions of FTRs are deferred as a regulatory asset or liability. Given this regulatory treatment and the limited magnitude of FTRs relative to the electric utility operations of SPS, the numerous unobservable quantitative inputs pertinent to the value of FTRs are insignificant to the financial statements of SPS.

Derivative Instruments Fair Value Measurements

SPS enters into derivative instruments, including forward contracts, for trading purposes and to manage risk in connection with changes in interest rates and electric utility commodity prices.

Interest Rate Derivatives — SPS may enter into various instruments that effectively fix the interest payments on certain floating rate debt obligations or effectively fix the yield or price on a specified benchmark interest rate for an anticipated debt issuance for a specific period. These derivative instruments are generally designated as cash flow hedges for accounting purposes. As of March 31, 2019, accumulated other comprehensive losses related to interest rate derivatives included $0.1 million net losses expected to be reclassified into earnings during the next 12 months as the related hedged interest rate transactions impact earnings, including forecasted amounts for unsettled hedges, as applicable.

Wholesale and Commodity Trading Risk — SPS conducts various wholesale and commodity trading activities, including the purchase and sale of electric capacity, energy and energy-related instruments, including derivatives. SPS is allowed to conduct these activities within guidelines and limitations as approved by its risk management committee, comprised of management personnel not directly involved in the activities governed by this policy.

Commodity Derivatives — SPS enters into derivative instruments to manage variability of future cash flows from changes in commodity prices in its electric utility operations. This could include the purchase or sale of energy or energy-related products and FTRs.

Gross notional amounts of commodity FTRs:


^(a)	Amounts are not reflective of net positions in the underlying commodities.

Consideration of Credit Risk and Concentrations — SPS continuously monitors the creditworthiness of counterparties to its interest rate derivatives and commodity derivative contracts prior to settlement, and assesses each counterparty’s ability to perform on the transactions set forth in the contracts. Impact of credit risk was immaterial to the fair value of unsettled commodity derivatives presented in the balance sheets. SPS’ most significant concentrations of credit risk with particular entities or industries are contracts with counterparties to its wholesale, trading and non-trading commodity activities.

At March 31, 2019, one of the eight most significant counterparties for these activities, comprising $11.1 million or 24% of this credit exposure, had investment grade ratings from S&P Global Ratings, Moody’s Investor Services or Fitch Ratings. Five of the eight most significant counterparties, comprising $9.0 million or 20% of this credit exposure, were not rated by external rating agencies, but based on SPS’ internal analysis, had credit quality consistent with investment grade. Two of these significant counterparties, comprising $4.4 million or 10% of this credit exposure, had credit quality less than investment grade, based on external analysis. Six of these significant counterparties are municipal or cooperative electric entities, or other utilities.

Impact of Derivative Activities on Income and Accumulated Other Comprehensive Loss — Pre-tax losses related to interest rate derivatives reclassified from accumulated other comprehensive loss into earnings were immaterial for the three months ended March 31, 2019 and 2018.

Changes in the fair value of FTRs resulting in pre-tax net gains of $6.3 million and $0.3 million recognized for the three months ended March 31, 2019 and 2018, respectively, were reclassified as regulatory assets and liabilities. The classification as a regulatory asset or liability is based on expected recovery of FTR settlements through fuel and purchased energy cost recovery mechanisms.

FTR settlement gains of an immaterial amount and losses of $0.5 million were recognized for the three months ended March 31, 2019 and 2018, respectively, and were recorded to electric fuel and purchased power. These derivative settlement gains and losses are shared with electric customers through fuel and purchased energy cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

SPS had no derivative instruments designated as fair value hedges during the three months ended March 31, 2019 and 2018.

Recurring Fair Value Measurements — SPS’ derivative assets and liabilities measured at fair value on a recurring basis:



	March 31, 2019												Dec. 31, 2018
	Fair Value												Fair Value
(Millions of Dollars)	Level 1		Level 2		Level 3		Fair Value Total		Netting ^(a)		Total		Level 1		Level 2		Level 3		Fair Value Total		Netting ^(a)			Total
Current derivative assets
Other derivative instruments:
Electric commodity	$	—	$	—	$	3.1	$	3.1	$	—	$	3.1	$	—	$	—	$	14.9	$	14.9	$	(0.2	)	$	14.7
Total current derivative assets	$	—	$	—	$	3.1	$	3.1	$	—	3.1		$	—	$	—	$	14.9	$	14.9	$	(0.2	)	14.7
PPAs ^(b)											3.1													3.1
Current derivative instruments											$	6.2												$	17.8
Noncurrent derivative assets
PPAs ^(b)											15.0													15.8
Noncurrent derivative instruments											$	15.0												$	15.8
Current derivative liabilities
Other derivative instruments:
Electric commodity	$	—	$	—	$	—	$	—	$	—	$	—	$	—	$	—	$	0.2	$	0.2	$	(0.2	)	$	—
Total current derivative liabilities	$	—	$	—	$	—	$	—	$	—	—		$	—	$	—	$	0.2	$	0.2	$	(0.2	)	—
PPAs ^(b)											3.6								.					3.6
Current derivative instruments											$	3.6												$	3.6
Noncurrent derivative liabilities
PPAs ^(b)											15.5													16.4
Noncurrent derivative instruments											$	15.5												$	16.4

^(a)

SPS nets derivative instruments and related collateral in its balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at March 31, 2019 and Dec. 31, 2018. At both March 31, 2019 and Dec. 31, 2018, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting excludes settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.


^(b)	During 2006, SPS qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

Changes in Level 3 commodity derivatives for the three months ended March 31, 2019 and 2018:



	Three Months Ended March 31,
(Millions of Dollars)	2019			2018
Balance at Jan. 1	$	14.7		$	12.7
Purchases	3.9			0.7
Settlements	(6.5		)	(10.4		)
Net transactions recorded during the period:
Net (losses) gains recognized as regulatory assets and liabilities	(9.0		)	2.4
Balance at March 31	$	3.1		$	5.4

SPS recognizes transfers between fair value hierarchy levels as of the beginning of each period. There were no transfers of amounts between levels for derivative instruments for the three months ended March 31, 2019 and 2018.

Fair Value of Long-Term Debt

Other financial instruments for which the carrying amount did not equal fair value:



	March 31, 2019				Dec. 31, 2018
(Millions of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt, including current portion	$	2,126.3	$	2,220.4	$	2,126.1	$	2,139.8

Fair value of SPS’ long-term debt is estimated based on recent trades and observable spreads from benchmark interest rates for similar securities. Fair value estimates are based on information available to management as of March 31, 2019 and Dec. 31, 2018, and given the observability of the inputs, the fair values presented for long-term debt were assigned as Level 2.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Benefit Plans and Other Postretirement Benefits

3 Months Ended

Mar. 31, 2019

Retirement Benefits [Abstract]

Benefit Plans and Other Postretirement Benefits

Components of Net Periodic Benefit Cost (Credit)



	Three Months Ended March 31
	2019			2018			2019			2018
(Millions of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	2.2		$	2.4		$	0.2		$	0.3
Interest cost ^(a)	5.0			4.6			0.4			0.4
Expected return on plan assets ^(a)	(7.2		)	(7.1		)	(0.5		)	(0.6		)
Amortization of prior service credit ^(a)	—			—			(0.1		)	(0.1		)
Amortization of net loss (gain) ^(a)	2.8			3.5			(0.1		)	(0.2		)
Net periodic benefit cost (credit)	2.8			3.4			(0.1		)	(0.2		)
(Costs) credits not recognized due to the effects of regulation	0.4			1.0			—			—
Net benefit cost (credit) recognized for financial reporting	$	3.2		$	4.4		$	(0.1	)	$	(0.2	)

^(a)The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the income statement or capitalized on the balance sheet as a regulatory asset.

In January 2019, contributions of $150 million were made across four of Xcel Energy’s pension plans, of which $17 million was attributable to SPS. Xcel Energy does not expect additional pension contributions during 2019.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2019

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

The following include commitments, contingencies and unresolved contingencies that are material to SPS’ financial position.

Legal

SPS is involved in various litigation matters that are being defended and handled in the ordinary course of business. The assessment of whether a loss is probable or is a reasonable possibility, and whether the loss or a range of loss is estimable, often involves complex judgments about future events. Management maintains accruals for losses that are probable of being incurred and subject to reasonable estimation. Management is sometimes unable to estimate an amount or range of a reasonably possible loss in certain situations, including when (1) the damages sought are indeterminate, (2) the proceedings are in the early stages or (3) the matters involve novel or unsettled legal theories. In such cases, there is considerable uncertainty regarding the timing or ultimate resolution of such matters, including a possible eventual loss.

For current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on SPS’ financial statements. Unless otherwise required by GAAP, legal fees are expensed as incurred.

Rate Matters

SPP OATT Upgrade Costs — Under the SPP OATT, costs of transmission upgrades may be recovered from other SPP customers whose transmission service depends on capacity enabled by the upgrade. SPP had not been charging its customers for these upgrades, even though the SPP OATT had allowed SPP to do so since 2008. In 2016, the FERC granted SPP’s request to recover these previously unbilled charges and SPP subsequently billed SPS approximately $13 million.

In July 2018, SPS’ appeal to the D.C. Circuit over the FERC rulings granting SPP the right to recover these previously unbilled charges was remanded to the FERC. In February 2019, after submission of additional briefs, the FERC reversed its 2016 decision and ordered SPP to refund the charges retroactively collected from its transmission customers, including SPS, related to periods before Sept. 2015. On April 1, 2019, several parties, including SPP, filed requests for rehearing. The timing of a FERC response to the rehearing requests is uncertain. The refunds are expected to be given back to SPS customers through future rates.

In October 2017, SPS filed a separate complaint against SPP asserting that SPP has assessed upgrade charges to SPS in violation of the SPP OATT. The FERC granted a rehearing for further consideration in May 2018. The timing of FERC action on the SPS rehearing is uncertain. If SPS’ complaint results in additional charges or refunds, SPS will seek to recover or refund the amounts through future SPS customer rates.

SPP Filing to Assign GridLiance Facilities to SPS Rate Zone — In August 2018, SPP filed a request with the FERC to amend its OATT to include the costs of the GridLiance High Plains, LLC. facilities in the SPS rate zone. In a previous filing, the FERC determined that some of these facilities did not qualify as transmission facilities under the SPP OATT. SPP’s proposed tariff changes could result in an increase in the ATRR of $9.5 million per year, with $6 million allocated to SPS’ retail customers.

The remaining $3.5 million would be paid by other wholesale loads in the SPS rate zone. In September 2018, SPS protested the proposed SPP tariff charges, and asked the FERC to reject the SPP filing. On October 31, 2018, the FERC issued an order accepting the proposed charges as of November 1, 2018. In December 2018, the FERC hosted a settlement hearing over the matter. A hearing will be ordered if a settlement is not reached.

SPS Filing to Modify Wholesale Transmission Rates - In 2018, SPS filed revisions to its wholesale transmission formula rate. The proposal includes an update to the depreciation rates for transmission plant. The new formula rate would provide flow-back of “excess” ADIT resulting from the TCJA and recover certain wholesale regulatory commission expenses.

The proposed changes would increase wholesale transmission revenues by approximately $9.4 million, with approximately $4.4 million of the total being recovered in SPP regional transmission rates. SPS proposed that the formula rate changes be effective February 1, 2019.

In January 2019, the FERC issued an order accepting the proposed rate changes as of February 1, 2019, subject to refund and settlement procedures. The first settlement conference is expected in April 2019.

Environmental

MGP, Landfill or Disposal Sites — SPS is currently investigating or remediating a MGP, landfill or other disposal site across its service territories, and these activities will continue through at least 2020. SPS accrued $0.1 million as of March 31, 2019 and Dec. 31, 2018, respectively. There may be insurance recovery and/or recovery from other potentially responsible parties, offsetting a portion of the costs incurred.

Leases

SPS evaluates a variety of contracts that may contain leases, including PPAs and arrangements for the use of office space and other facilities, vehicles and equipment. Under ASC Topic 842, adopted by SPS on Jan. 1, 2019, a contract contains a lease if it conveys the exclusive right to control the use of a specific asset. A contract determined to contain a lease is evaluated further to determine if the arrangement is a finance lease.

ROU assets represent SPS’ rights to use leased assets. Starting in 2019, the present value of future operating lease payments are recognized in other current liabilities and noncurrent operating lease liabilities. These amounts, adjusted for any prepayments or incentives, are recognized as operating lease ROU assets.

Most of SPS’ leases do not contain a readily determinable discount rate, and therefore the present value of future lease payments is calculated using the estimated incremental borrowing rate for similar borrowing periods. SPS has elected the practical expedient under which non-lease components, such as asset maintenance costs included in payments to the lessor, are not deducted from minimum lease payments for the purposes of lease accounting and disclosure. Leases with an initial term of 12 months or less are classified as short-term leases and are not recognized on the balance sheet.

Operating lease ROU assets:



(Millions of Dollars)	March 31, 2019
PPAs	$	500.3
Other	48.0
Gross operating lease ROU assets	548.3
Accumulated amortization	(6.3		)
Net operating lease ROU assets	$	542.0

Given the impacts of accounting for regulated operations, and the resulting recognition of periodic expense at the amounts recovered in customer rates, cash expenditures for operating leases are consistent with recognized lease expense.

Components of lease expense:



(Millions of Dollars)	Three Months Ended March 31, 2019
Operating leases
PPA capacity payments	$	12.8
Other operating leases ^(a)	1.2
Total operating lease expense ^(b)	$	14.0


^(a)	Includes short-term lease expense of $0.4 million.


^(b)	PPA capacity payments are included in electric fuel and purchased power on the statements of income. Expense for other operating leases is included in O&M expense.

Future commitments under operating leases as of March 31, 2019:



(Millions of Dollars)	PPA ^{(a) (b)} Operating Leases			Other Operating Leases			Total Operating Leases
2019	$	34.7		$	2.5		$	37.2
2020	46.2			3.4			49.6
2021	46.2			3.3			49.5
2022	46.2			3.4			49.6
2023	46.2			3.4			49.6
Thereafter	450.8			54.8			505.6
Total minimum obligation	670.3			70.8			741.1
Interest component of obligation	(176.0		)	(23.1		)	(199.1		)
Present value of minimum obligation	494.3			47.7			542.0
Less current portion							(26.2		)
Noncurrent operating lease liabilities							$	515.8

Weighted-average discount rate							4.4		%
Weighted-average remaining lease term in years							14.8


^(a)	Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs.


^(b)	PPA operating leases contractually expire at various dates through 2033.

Future commitments under operating leases as of Dec. 31, 2018:



(Millions of Dollars)	PPA ^{(a) (b)} Operating Leases		Other Operating Leases		Total Operating Leases
2019	$	46.7	$	5.2	$	51.9
2020	46.2		5.2		51.4
2021	46.2		5.1		51.3
2022	46.2		5.1		51.3
2023	46.2		5.1		51.3
Thereafter	450.8		56.3		507.1


^(a)	Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs.


^(b)	PPA operating leases contractually expire at various dates through 2033.

Variable Interest Entities

Under certain PPAs, SPS purchases power from IPPs for which SPS is required to reimburse fuel costs, or to participate in tolling arrangements under which SPS procures the natural gas required to produce the energy that it purchases. These specific PPAs create a variable interest in the associated IPP.

SPS had approximately 1,197 MW of capacity under long-term PPAs as of March 31, 2019 and Dec. 31, 2018, with entities that have been determined to be VIEs. SPS concluded that these entities are not required to be consolidated in its financial statements because it does not have the power to direct the activities that most significantly impact the entities’ economic performance. These agreements have expiration dates through 2041.

Selected Balance Sheet Data (Tables)

3 Months Ended

Mar. 31, 2019

Balance Sheet Related Disclosures [Abstract]

Accounts Receivable, Net



(Millions of Dollars)	March 31, 2019			Dec. 31, 2018
Accounts receivable, net
Accounts receivable	$	98.7		$	96.3
Less allowance for bad debts	(5.5		)	(5.6		)
	$	93.2		$	90.7

Inventories



(Millions of Dollars)	March 31, 2019		Dec. 31, 2018
Inventories
Materials and supplies	$	25.8	$	25.7
Fuel	8.5		8.2
	$	34.3	$	33.9

Property, Plant and Equipment, Net



(Millions of Dollars)	March 31, 2019			Dec. 31, 2018
Property, plant and equipment, net
Electric plant	$	7,287.2		$	7,227.7
Construction work in progress	974.3			847.3
Total property, plant and equipment	8,261.5			8,075.0
Less accumulated depreciation	(2,173.0		)	(2,128.6		)
Total	$	6,088.5		$	5,946.4

Borrowings and Other Financing Instruments (Tables)

3 Months Ended

Mar. 31, 2019

Borrowings and Other Financing Instruments [Abstract]

Credit Facilities

As of March 31, 2019, SPS had the following committed credit facility available (in millions of dollars):



Credit Facility ^(a)		Outstanding ^(b)		Available
$	400	$	139	$	261


^(a)	This credit facility expires in June 2021.


^(b)	Includes outstanding commercial paper and letters of credit.

All credit facility bank borrowings, outstanding letters of credit and outstanding commercial paper reduce the available capacity under the credit facility. SPS had no direct advances on the credit facility outstanding as of March 31, 2019 and Dec. 31, 2018.

.

Money Pool

Borrowings and Other Financing Instruments [Abstract]

Short-Term Borrowings

Money pool borrowings for SPS were as follows:



(Amounts in Millions, Except Interest Rates)	Three Months Ended March 31, 2019			Year Ended Dec. 31, 2018
Borrowing limit	$	100		$	100
Amount outstanding at period end	38			—
Average amount outstanding	19			29
Maximum amount outstanding	100			100
Weighted average interest rate, computed on a daily basis	2.44		%	1.96		%
Weighted average interest rate at period end	2.44			N/A

Commercial Paper

Borrowings and Other Financing Instruments [Abstract]

Short-Term Borrowings

Commercial paper outstanding for SPS was as follows:



(Amounts in Millions, Except Interest Rates)	Three Months Ended March 31, 2019			Year Ended Dec. 31, 2018
Borrowing limit	$	400		$	400
Amount outstanding at period end	137			42
Average amount outstanding	86			30
Maximum amount outstanding	152			144
Weighted average interest rate, computed on a daily basis	2.69		%	2.27		%
Weighted average interest rate at period end	2.71			2.80

Revenues (Tables)

3 Months Ended

Mar. 31, 2019

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

SPS’ operating revenues consists of the following:



	Three Months Ended
(Millions of Dollars)	March 31, 2019		March 31, 2018
Major revenue types
Revenue from contracts with customers:
Residential	$	88.1	$	80.0
C&I	205.8		195.8
Other	9.6		9.7
Total retail	303.5		285.5
Wholesale	84.8		93.2
Transmission	57.4		55.7
Other	1.0		7.5
Total revenue from contracts with customers	446.7		441.9
Alternative revenue and other	7.4		5.3
Total revenues	$	454.1	$	447.2

Income Taxes (Tables)

3 Months Ended

Mar. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

Total income tax expense from operations differs from the amount computed by applying the statutory federal income tax rate to income before income tax expense. The following reconciles such differences:



	Three Months Ended March 31,
	2019		2018
Federal statutory rate	21.0	%	21.0	%
State tax (net of federal tax effect)	2.1		2.4
Increases (decreases) in tax from:
Regulatory differences ^(a)	(4.6	)	(2.7	)
Tax credits (net)	(0.6	)	(0.7	)
Other (net)	(0.7	)	—
Effective income tax rate	17.2	%	20.0	%

^(a)

Regulatory differences for income tax purposes primarily include the average rate assumption method (ARAM), ARAM deferral and AFUDC - Equity. ARAM is a method to flow back excess deferred taxes to customers. ARAM has been deferred when regulatory treatment has not been established. As Xcel Energy received direction from its regulatory commissions regarding the return of excess deferred taxes to customers, the ARAM deferral was reversed. This resulted in a reduction to tax expense with a corresponding reduction to revenue.

Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block]

Federal Audits — SPS is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. Statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows:



Tax Year(s)		Expiration
2009 - 2013		October 2019
2014 - 2016		September 2020
2017		September 2021

Reconciliation of Unrecognized Tax Benefits

Unrecognized tax benefits - permanent vs temporary:



(Millions of Dollars)	March 31, 2019		Dec. 31, 2018
Unrecognized tax benefit — Permanent tax positions	$	3.1	$	3.0
Unrecognized tax benefit — Temporary tax positions	1.6		1.5
Total unrecognized tax benefit	$	4.7	$	4.5

Tax Benefits Associated with NOL and Tax Credit Carryforwards

Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards:



(Millions of Dollars)	March 31, 2019			Dec. 31, 2018
NOL and tax credit carryforwards	$	(4.0	)	$	(3.8	)

Interest Payable related to Unrecognized Tax Benefits [Table Text Block]

Interest payable related to unrecognized tax benefits:



(Millions of Dollars)	March 31, 2019		Dec. 31, 2018
Receivable for interest related to unrecognized tax benefits at beginning of period	$	0.7	$	0.5
Interest income related to unrecognized tax benefits	—		0.2
Receivable for interest related to unrecognized tax benefits at end of period	$	0.7	$	0.7

Fair Value of Financial Assets and Liabilities (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Gross Notional Amounts of Commodity FTRs

Gross notional amounts of commodity FTRs:


^(a)	Amounts are not reflective of net positions in the underlying commodities.

Derivative Assets and Liabilities Measured at Fair Value on a Recurring Basis by Hierarchy Level

Recurring Fair Value Measurements — SPS’ derivative assets and liabilities measured at fair value on a recurring basis:



	March 31, 2019												Dec. 31, 2018
	Fair Value												Fair Value
(Millions of Dollars)	Level 1		Level 2		Level 3		Fair Value Total		Netting ^(a)		Total		Level 1		Level 2		Level 3		Fair Value Total		Netting ^(a)			Total
Current derivative assets
Other derivative instruments:
Electric commodity	$	—	$	—	$	3.1	$	3.1	$	—	$	3.1	$	—	$	—	$	14.9	$	14.9	$	(0.2	)	$	14.7
Total current derivative assets	$	—	$	—	$	3.1	$	3.1	$	—	3.1		$	—	$	—	$	14.9	$	14.9	$	(0.2	)	14.7
PPAs ^(b)											3.1													3.1
Current derivative instruments											$	6.2												$	17.8
Noncurrent derivative assets
PPAs ^(b)											15.0													15.8
Noncurrent derivative instruments											$	15.0												$	15.8
Current derivative liabilities
Other derivative instruments:
Electric commodity	$	—	$	—	$	—	$	—	$	—	$	—	$	—	$	—	$	0.2	$	0.2	$	(0.2	)	$	—
Total current derivative liabilities	$	—	$	—	$	—	$	—	$	—	—		$	—	$	—	$	0.2	$	0.2	$	(0.2	)	—
PPAs ^(b)											3.6								.					3.6
Current derivative instruments											$	3.6												$	3.6
Noncurrent derivative liabilities
PPAs ^(b)											15.5													16.4
Noncurrent derivative instruments											$	15.5												$	16.4

^(a)

SPS nets derivative instruments and related collateral in its balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at March 31, 2019 and Dec. 31, 2018. At both March 31, 2019 and Dec. 31, 2018, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting excludes settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.


^(b)	During 2006, SPS qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

Changes in Level 3 Commodity Derivatives

Changes in Level 3 commodity derivatives for the three months ended March 31, 2019 and 2018:



	Three Months Ended March 31,
(Millions of Dollars)	2019			2018
Balance at Jan. 1	$	14.7		$	12.7
Purchases	3.9			0.7
Settlements	(6.5		)	(10.4		)
Net transactions recorded during the period:
Net (losses) gains recognized as regulatory assets and liabilities	(9.0		)	2.4
Balance at March 31	$	3.1		$	5.4

Carrying Amount and Fair Value of Long-term Debt

Other financial instruments for which the carrying amount did not equal fair value:



	March 31, 2019				Dec. 31, 2018
(Millions of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt, including current portion	$	2,126.3	$	2,220.4	$	2,126.1	$	2,139.8

Benefit Plans and Other Postretirement Benefits (Tables)

3 Months Ended

Mar. 31, 2019

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost (Credit)



	Three Months Ended March 31
	2019			2018			2019			2018
(Millions of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	2.2		$	2.4		$	0.2		$	0.3
Interest cost ^(a)	5.0			4.6			0.4			0.4
Expected return on plan assets ^(a)	(7.2		)	(7.1		)	(0.5		)	(0.6		)
Amortization of prior service credit ^(a)	—			—			(0.1		)	(0.1		)
Amortization of net loss (gain) ^(a)	2.8			3.5			(0.1		)	(0.2		)
Net periodic benefit cost (credit)	2.8			3.4			(0.1		)	(0.2		)
(Costs) credits not recognized due to the effects of regulation	0.4			1.0			—			—
Net benefit cost (credit) recognized for financial reporting	$	3.2		$	4.4		$	(0.1	)	$	(0.2	)

^(a)The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the income statement or capitalized on the balance sheet as a regulatory asset.

Commitments and Contingencies Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2019

Commitments and Contingencies Disclosure [Abstract]

Schedule of Operating Lease Right-of-Use Assets

Operating lease ROU assets:



(Millions of Dollars)	March 31, 2019
PPAs	$	500.3
Other	48.0
Gross operating lease ROU assets	548.3
Accumulated amortization	(6.3		)
Net operating lease ROU assets	$	542.0

Schedule of Components of Lease Expense

Components of lease expense:



(Millions of Dollars)	Three Months Ended March 31, 2019
Operating leases
PPA capacity payments	$	12.8
Other operating leases ^(a)	1.2
Total operating lease expense ^(b)	$	14.0


^(a)	Includes short-term lease expense of $0.4 million.


^(b)	PPA capacity payments are included in electric fuel and purchased power on the statements of income. Expense for other operating leases is included in O&M expense.

Schedule of Future Commitments under Operating Leases

Future commitments under operating leases as of March 31, 2019:



(Millions of Dollars)	PPA ^{(a) (b)} Operating Leases			Other Operating Leases			Total Operating Leases
2019	$	34.7		$	2.5		$	37.2
2020	46.2			3.4			49.6
2021	46.2			3.3			49.5
2022	46.2			3.4			49.6
2023	46.2			3.4			49.6
Thereafter	450.8			54.8			505.6
Total minimum obligation	670.3			70.8			741.1
Interest component of obligation	(176.0		)	(23.1		)	(199.1		)
Present value of minimum obligation	494.3			47.7			542.0
Less current portion							(26.2		)
Noncurrent operating lease liabilities							$	515.8

Weighted-average discount rate							4.4		%
Weighted-average remaining lease term in years							14.8


^(a)	Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs.


^(b)	PPA operating leases contractually expire at various dates through 2033.

Future commitments under operating leases as of Dec. 31, 2018:



(Millions of Dollars)	PPA ^{(a) (b)} Operating Leases		Other Operating Leases		Total Operating Leases
2019	$	46.7	$	5.2	$	51.9
2020	46.2		5.2		51.4
2021	46.2		5.1		51.3
2022	46.2		5.1		51.3
2023	46.2		5.1		51.3
Thereafter	450.8		56.3		507.1


^(a)	Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs.


^(b)	PPA operating leases contractually expire at various dates through 2033.

Summary of Significant Accounting Policies accounting policies (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Public Utilities, Inventory [Line Items]
Public Utilities, Inventory	$ 34.3	$ 33.9
Allowance for Doubtful Accounts Receivable, Current	5.5	5.6
Public Utilities, Inventory, Fuel [Member]
Public Utilities, Inventory [Line Items]
Public Utilities, Inventory	8.5	8.2
Supplies [Member]
Public Utilities, Inventory [Line Items]
Public Utilities, Inventory	$ 25.8	$ 25.7

Accounting Pronouncements (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset	$ 542.0		$ 0.0
Operating Lease, Liability	$ 542.0
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset		$ 500.0
Operating Lease, Liability		$ 500.0

Selected Balance Sheet Data (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Accounts receivable, net
Accounts receivable	$ 98.7	$ 96.3
Less allowance for bad debts	(5.5)	(5.6)
Accounts receivable, net	$ 93.2	$ 90.7

Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 8,261.5	$ 8,075.0
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	2,173.0	2,128.6
Property, Plant and Equipment, Net	6,088.5	5,946.4
Electric Generation Equipment [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	7,287.2	7,227.7
Construction in Progress [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 974.3	$ 847.3

Selected Balance Sheet Data Inventory (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Public Utilities, Inventory	$ 34.3	$ 33.9
Supplies [Member]
Public Utilities, Inventory	25.8	25.7
Public Utilities, Inventory, Fuel [Member]
Public Utilities, Inventory	$ 8.5	$ 8.2

Borrowings and Other Financing Instruments, Short-Term Borrowings (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Amount outstanding at period end	$ 137,000,000	$ 42,000,000
Money Pool
Short-term Debt [Line Items]
Borrowing limit	100,000,000	100,000,000
Amount outstanding at period end	38,000,000	0
Average amount outstanding	19,000,000	29,000,000
Maximum amount outstanding	$ 100,000,000	$ 100,000,000
Weighted average interest rate, computed on a daily basis (percentage)	2.44%	1.96%
Weighted average interest rate at period end (percentage)	2.44%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 400,000,000	$ 400,000,000
Amount outstanding at period end	137,000,000	42,000,000
Average amount outstanding	86,000,000	30,000,000
Maximum amount outstanding	$ 152,000,000	$ 144,000,000
Weighted average interest rate, computed on a daily basis (percentage)	2.69%	2.27%
Weighted average interest rate at period end (percentage)	2.71%	2.80%

Borrowings and Other Financing Instruments, Letters of Credit (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 137.0	$ 42.0
Letter of Credit
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 2.0	$ 2.0
Letter of Credit \| Letter of Credit
Line of Credit Facility [Line Items]
Term of letters of credit (in years)	1 year

Borrowings and Other Financing Instruments, Credit Facility (Details) - Credit Facility - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Credit Facility	$ 400,000,000
Drawn	139,000,000
Available	261,000,000
Direct advances on the credit facility outstanding	$ 0	$ 0

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

Revenues (Details) - USD ($) $ in Millions	3 Months Ended
Revenues (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Operating revenues	$ 454.1	$ 447.2
Regulated Electric [Member] \| Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	446.7	441.9
Regulated Electric [Member] \| Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	303.5	285.5
Regulated Electric [Member] \| Retail \| Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	88.1	80.0
Regulated Electric [Member] \| Retail \| Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	205.8	195.8
Regulated Electric [Member] \| Retail \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	9.6	9.7
Regulated Electric [Member] \| Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	84.8	93.2
Regulated Electric [Member] \| Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	57.4	55.7
Regulated Electric [Member] \| Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1.0	7.5
Regulated Electric [Member] \| Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Operating revenues	7.4	5.3
Total revenues \| Regulated Electric [Member]
Disaggregation of Revenue [Line Items]
Operating revenues	$ 454.1	$ 447.2

Income Taxes (Details) - USD ($)

3 Months Ended

12 Months Ended

Mar. 31, 2019

Dec. 31, 2018

Mar. 31, 2018

Sep. 30, 2017

Sep. 30, 2015

Dec. 31, 2018

Tax Audits [Abstract]

Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent

21.00%

Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent

2.10%

2.40%

Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent

^[1]

(4.60%)

(2.70%)

Regulatory differences - reversal of prior quarters' ARAM deferral (b)

(0.60%)

(0.70%)

Effective Income Tax Rate Reconciliation, Other Adjustments, Percent

(0.70%)

0.00%

Effective Income Tax Rate Reconciliation, Percent

17.20%

20.00%

Unrecognized Tax Benefits [Abstract]

Unrecognized tax benefit - Permanent tax positions

$ 3,100,000

$ 3,000,000

Unrecognized tax benefit - Temporary tax positions

1,600,000

1,500,000

Total unrecognized tax benefit

4,700,000

4,500,000

NOL and tax credit carryforwards

(4,000,000)

(3,800,000)

Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards

(900,000)

(800,000)

Upper bound of decrease in unrecognized tax benefit that is reasonably possible

3,600,000

Amounts accrued for penalties related to unrecognized tax benefits

0

Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]

Receivable for interest related to unrecognized tax benefits at beginning of period

700,000

$ 500,000

500,000

Interest income related to unrecognized tax benefits

0

200,000

Receivable for interest related to unrecognized tax benefits at end of period

700,000

$ 700,000

Internal Revenue Service (IRS)

Tax Audits [Abstract]

Year(s) under examination

2014 - 2016

2012 and 2013

Tax years under examination, Concluded

2012 and 2013

Potential Tax Adjustments

$ 0

TEXAS

Tax Audits [Abstract]

Earliest year subject to examination

2009

[1]

Regulatory differences for income tax purposes primarily include the average rate assumption method (ARAM), ARAM deferral and AFUDC - Equity. ARAM is a method to flow back excess deferred taxes to customers. ARAM has been deferred when regulatory treatment has not been established. As Xcel Energy received direction from its regulatory commissions regarding the return of excess deferred taxes to customers, the ARAM deferral was reversed. This resulted in a reduction to tax expense with a corresponding reduction to revenue.

Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details)
MWh in Millions, $ in Millions

Mar. 31, 2019

USD ($)

MWh

Counterparty

Dec. 31, 2018

MWh

Credit Concentration Risk

Consideration of Credit Risk and Concentrations [Abstract]

Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure

8

Credit Concentration Risk | Municipal or Cooperative Entities or Other Utilities [Member]

Consideration of Credit Risk and Concentrations [Abstract]

Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure

6

Credit Concentration Risk | External Credit Rating, Investment Grade [Member]

Consideration of Credit Risk and Concentrations [Abstract]

Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure

1

Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $

$ 11.1

Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)

24.00%

Credit Concentration Risk | No Investment Grade Ratings from External Credit Rating Agencies [Member]

Consideration of Credit Risk and Concentrations [Abstract]

Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure

5

Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $

$ 9.0

Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)

20.00%

Credit Concentration Risk | External Credit Rating, Non Investment Grade [Member]

Consideration of Credit Risk and Concentrations [Abstract]

Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure

2

Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $

$ 4.4

Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)

10.00%

Interest Rate Swap [Member]

Derivative [Line Items]

Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net | $

$ (0.1)

Electric Commodity (in megawatt hours)

Gross Notional Amounts of Commodity FTRs [Abstract]

Derivative, Nonmonetary Notional amount | MWh

^[1]

2.2

5.5

[1]	Amounts are not reflective of net positions in the underlying commodities.

Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]
Derivative instruments designated as fair value hedges	$ 0.0	$ 0.0
Other Derivative Instruments \| Electric Commodity
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	$ 6.3	0.3
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		$ 0.5

Fair Value of Financial Assets and Liabilities, Fair Value Measurements (Details) - USD ($)
$ in Millions

Mar. 31, 2019

Dec. 31, 2018

Derivatives, Fair Value [Line Items]

Derivative Asset, Collateral, Obligation to Return Cash, Offset

$ 0.0

Derivative Liability, Collateral, Right to Reclaim Cash, Offset

0.0

Other Current Assets

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

6.2

17.8

Other Noncurrent Assets [Member]

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

15.0

15.8

Other Current Liabilities

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

3.6

Other Noncurrent Liabilities [Member]

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

15.5

16.4

Fair Value Measured on a Recurring Basis | Other Current Assets

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

3.1

14.7

Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset

^[1]

0.0

(0.2)

Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

3.1

14.7

Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset

^[1]

0.0

(0.2)

Fair Value Measured on a Recurring Basis | Other Current Liabilities

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset

^[1]

0.0

(0.2)

Derivative Liability, Fair Value, Gross Liability

0.0

Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset

^[1]

0.0

(0.2)

Derivative Liability, Fair Value, Gross Liability

0.0

Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

0.0

Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

0.0

Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

0.0

Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

0.0

Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

0.0

Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

0.0

Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

0.0

Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

0.0

Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

3.1

14.9

Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

3.1

14.9

Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

0.0

0.2

Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

0.0

0.2

Fair Value, Measurements, Nonrecurring | Other Current Assets | PPAs

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

^[2]

3.1

Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets [Member] | PPAs

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

^[2]

15.0

15.8

Fair Value, Measurements, Nonrecurring | Other Current Liabilities | PPAs

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

^[2]

3.6

Fair Value, Measurements, Nonrecurring | Other Noncurrent Liabilities [Member] | PPAs

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

^[2]

15.5

16.4

Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

3.1

14.9

Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Asset, Fair Value, Gross Asset

3.1

14.9

Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

0.0

0.2

Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Electric Commodity

Derivatives, Fair Value [Line Items]

Derivative Liability, Fair Value, Gross Liability

$ 0.0

$ 0.2

[1]

SPS nets derivative instruments and related collateral in its balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at March 31, 2019 and Dec. 31, 2018. At both March 31, 2019 and Dec. 31, 2018, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting excludes settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

[2]

During 2006, SPS qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) - Commodity Contract - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 14.7	$ 12.7
Purchases	3.9	0.7
Settlements	(6.5)	(10.4)
Net gains recognized as regulatory assets and liabilities	(9.0)	2.4
Balance at end of period	3.1	5.4
Transfers into Level 3	0.0	0.0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3	$ 0.0	$ 0.0

Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Carrying Amount
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 2,126.3	$ 2,126.1
Fair Value
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 2,220.4	$ 2,139.8

Benefit Plans and Other Postretirement Benefits (Details) $ in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2019 USD ($) Plan	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Pension Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 2.2	$ 2.4
Interest cost		5.0	4.6
Expected return on plan assets		(7.2)	(7.1)
Amortization of prior service cost (credit)		0.0	0.0
Amortization of net loss (gain)		2.8	3.5
Net periodic benefit cost (credit)		2.8	3.4
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0.4	1.0
Net benefit cost (credit) recognized for financial reporting		3.2	4.4
Total contributions to the pension plans during the period	$ 17.0
Pension Plan [Member] \| Xcel Energy Inc.
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Total contributions to the pension plans during the period	$ 150.0
Number of Xcel Energy's pension plans to which contributions were made \| Plan	4
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.2	0.3
Interest cost		0.4	0.4
Expected return on plan assets		(0.5)	(0.6)
Amortization of prior service cost (credit)		(0.1)	(0.1)
Amortization of net loss (gain)		(0.1)	(0.2)
Net periodic benefit cost (credit)		(0.1)	(0.2)
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation		0.0	0.0
Net benefit cost (credit) recognized for financial reporting		$ (0.1)	$ (0.2)

Commitments and Contingencies, Purchased Power Agreements (Details) - Independent Power Producing Entities - MW	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Purchased Power Agreements [Abstract]
Generating capacity (in MW)	1,197	1,197
Purchase Power Agreement Expiration (year)	2041	2041

Commitments and Contingencies Commitments and Contingencies, Environmental Contingencies - Site Contingencies (Details) $ in Millions	Mar. 31, 2019 USD ($)
Other MGP, Landfill, or Disposal Sites [Domain]
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies	$ 0.1

Commitments and Contingencies, Rate Matters, SPS (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Aug. 31, 2018	Dec. 31, 2018	Dec. 31, 2016	Mar. 31, 2019
Public Utilities, General Disclosures [Line Items]
Public Utilities, Amount proposed changes would increase wholesale transmission revenues		$ 9.4
Public Utilities, Amount of proposed changes would be recoverable		$ 4.4
Southwest Power Pool (SPP) \| SPP Open Access Transmission Tariff Upgrade Costs
Public Utilities, General Disclosures [Line Items]
Public Utilities, Annual Transmission Revenue Requirement Increase	$ 9.5
Public Utilities, Annual Transmission Revenue Requirement Increase (SPS)	6.0
Public Utilities, Annual Transmission Revenue Requirement (Other Utilities)	$ 3.5
SPS \| Southwest Power Pool (SPP) \| SPP Open Access Transmission Tariff Upgrade Costs
Public Utilities, General Disclosures [Line Items]
Public Utilities, Billed Charges For Transmission Service Upgrades			$ 13.0
Other MGP, Landfill, or Disposal Sites [Domain]
Public Utilities, General Disclosures [Line Items]
Accrual for Environmental Loss Contingencies				$ 0.1

Commitments and Contingencies Commitments and Contingencies, Leases - Right-of-Use Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Maximum lease term for short-term lease classification	12 months
Operating Lease, Right-of-Use Asset, Gross	$ 548.3
Operating Lease, Right-of-Use Asset, Accumulated Depreciation	(6.3)
Operating Lease, Right-of-Use Asset	542.0	$ 0.0
PPAs
Lessee, Lease, Description [Line Items]
Operating Lease, Right-of-Use Asset, Gross	500.3
Other
Lessee, Lease, Description [Line Items]
Operating Lease, Right-of-Use Asset, Gross	$ 48.0

Commitments and Contingencies Commitments and Contingencies, Leases - Components of Lease Expense (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 14.0
Short-term Lease, Cost	0.4
PPAs
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	12.8
Other
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 1.2

Commitments and Contingencies Commitments and Contingencies, Leases - Future Commitments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Operating Leases after Adoption of ASC Topic 842
2019	$ 37.2
2020	49.6
2021	49.5
2022	49.6
2023	49.6
Thereafter	505.6
Total minimum obligation	741.1
Interest component of obligation	(199.1)
Present value of minimum obligation	542.0
Less current portion	(26.2)
Noncurrent operating lease liabilities	$ 515.8	$ 0.0
Weighted-average discount rate	4.40%
Weighted-average remaining lease term in years	14 years 10 months
Operating Leases before Adoption of ASC 842
2019		51.9
2020		51.4
2021		51.3
2022		51.3
2023		51.3
Thereafter		507.1
PPAs
Operating Leases after Adoption of ASC Topic 842
2019	$ 34.7
2020	46.2
2021	46.2
2022	46.2
2023	46.2
Thereafter	450.8
Total minimum obligation	670.3
Interest component of obligation	(176.0)
Present value of minimum obligation	494.3
Operating Leases before Adoption of ASC 842
2019		46.7
2020		46.2
2021		46.2
2022		46.2
2023		46.2
Thereafter		450.8
Other
Operating Leases after Adoption of ASC Topic 842
2019	2.5
2020	3.4
2021	3.3
2022	3.4
2023	3.4
Thereafter	54.8
Total minimum obligation	70.8
Interest component of obligation	(23.1)
Present value of minimum obligation	$ 47.7
Operating Leases before Adoption of ASC 842
2019		5.2
2020		5.2
2021		5.1
2022		5.1
2023		5.1
Thereafter		$ 56.3

Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income Tax Expense (Benefit)	$ 11.2	$ 8.3
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period	2,536.6
Accumulated other comprehensive loss at end of period	$ 2,533.2

(Amounts in Millions) ^(a)

March 31, 2019

Dec. 31, 2018

Megawatt hours of electricity