Southwestern Public Service 10-K 21 Feb 24 2023 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2023	Feb. 21, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Document Transition Report	false
Entity File Number	001-03789
Entity Incorporation, State or Country Code	NM
Entity Tax Identification Number	75-0575400
Entity Address, Address Line One	790 South Buchanan Street,
Entity Address, City or Town	Amarillo,
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	79101
City Area Code	(303)
Local Phone Number	571-7511
Entity Well-Known Season Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		100
Entity Registrant Name	SOUTHWESTERN PUBLIC SERVICE CO
Entity Central Index Key	0000092521
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Public Float			$ 0
Document Financial Statement Error Correction [Flag]	false

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2023
Auditor Information [Abstract]
Auditor Name	DELOITTE & TOUCHE LLP
Auditor Firm ID	34
Auditor Location	Minneapolis, Minnesota

Accounting Pronouncements

Accounting Pronouncements	12 Months Ended
	Dec. 31, 2023
Accounting Standards Update and Change in Accounting Principle [Abstract]
Accounting Pronouncements	Recently Issued Segment Reporting — In November 2023, the FASB issued ASU 2023-07 – Segment Reporting (Topic 280) – Improvements to Reportable Segment Disclosures , which extends the existing requirements for annual disclosures to quarterly periods, and requires that both annual and quarterly disclosures present segment expenses using line items consistent with information regularly provided to the chief operating decision maker. The ASU is effective for annual periods beginning after Dec. 15, 2023 and quarterly periods beginning after Dec. 15, 2024, and SPS does not expect implementation of the new disclosure guidance to have a material impact to its financial statements. Income Taxes — In December 2023, the FASB issued ASU 2023-09 – Income Taxes (Topic 740) – Improvements to Income Tax Disclosures

STATEMENTS OF INCOME

STATEMENTS OF INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues [Abstract]
Operating revenue	$ 2,152	$ 2,426	$ 2,465
Operating expenses
Electric fuel and purchased power	910	1,157	1,432
Operating and maintenance expenses	279	317	271
Demand side management program expenses	20	23	17
Depreciation and amortization	368	388	300
Taxes (other than income taxes)	100	107	79
Total operating expenses	1,686	1,992	2,099
Operating income	466	434	366
Other income (expense), net	2	0	1
Allowance for funds used during construction — equity	7	3	4
Interest charges and financing costs
Interest Expense	143	143	114
Allowance for funds used during construction — debt	(7)	(2)	(2)
Total interest charges and financing costs	136	141	112
Income before income taxes	339	296	259
Income taxes	(45)	(53)	(59)
Net income	384	349	318
Workforce Reduction Expense	$ 9	$ 0	$ 0

STATEMENTS OF INCOME (Parenthet

STATEMENTS OF INCOME (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Other financing costs	$ 4	$ 4	$ 4

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating activities
Net Income (Loss) Attributable to Parent	$ 384	$ 349	$ 318
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	373	391	303
Deferred income taxes	(133)	17	(47)
Allowance for equity funds used during construction	(7)	(3)	(4)
Provision for bad debts	11	9	6
Changes in operating assets and liabilities:
Accounts receivable	(67)	(67)	(29)
Increase (Decrease) in Accrued Unbilled Revenues	1	(16)	(10)
Inventories	(51)	(19)	(21)
Prepayments and other	39	(50)	16
Accounts payable	(37)	22	4
Net regulatory assets and liabilities	307	(5)	(154)
Other current liabilities	5	52	(1)
Pension and other employee benefit obligations	3	1	(18)
Other, net	(18)	(5)	(4)
Net cash provided by operating activities	810	676	359
Investing activities
Utility capital/construction expenditures	(714)	(578)	(580)
Investments in utility money pool arrangement	0	(176)	(83)
Receipts from utility money pool arrangement	0	176	83
Net cash used in investing activities	(714)	(578)	(580)
Financing activities
Proceeds from (repayments of) short-term borrowings, net	41	(103)	(113)
Proceeds from issuance of long-term debt	98	196	247
Borrowings under utility money pool arrangement	371	336	539
Repayments under utility money pool arrangement	(344)	(427)	(448)
Capital contributions from parent	48	220	301
Dividends paid to parent	(309)	(319)	(310)
Net cash provided by financing activities	(95)	(97)	216
Net change in cash and cash equivalents	1	1	(5)
Cash and cash equivalents at beginning of period	2	1	6
Cash and cash equivalents at end of period	3	2	1
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(127)	(137)	(108)
Cash paid for income taxes, net	(80)	81	21
Supplemental disclosure of non-cash investing transactions:
Accrued property, plant and equipment additions	56	86	37
Inventory transfers to plant, property and equipment	43	10	6
Allowance for Funds Used During Construction, Investing Activities	$ 7	$ 3	$ 4

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 3	$ 2
Accrued unbilled revenues	139	140
Inventories	69	61
Regulatory assets	30	217
Derivative instruments	42	122
Prepaid taxes	2	5
Prepayments and other	32	68
Total current assets	565	797
Property, plant and equipment, net	8,536	8,129
Other assets
Regulatory assets	349	359
Derivative instruments	0	3
Operating lease right-of-use assets	403	434
Other	28	26
Total other assets	780	822
Total assets	9,881	9,748
Long-Term Debt, Current Maturities	350	0
Current liabilities
Short-term debt	75	34
Borrowings under utility money pool arrangement	27	0
Regulatory liabilities	116	148
Taxes accrued	77	61
Accrued interest	33	31
Dividends payable to parent	59	61
Derivative instruments	2	4
Operating lease liabilities	32	31
Other	42	58
Total current liabilities	1,008	660
Deferred credits and other liabilities
Deferred income taxes	622	739
Regulatory liabilities	761	715
Asset retirement obligations	153	147
Derivative instruments	0	2
Pension and employee benefit obligations	12	12
Operating lease liabilities	371	403
Other	7	9
Total deferred credits and other liabilities	1,926	2,027
Commitments and contingencies
Capitalization
Long-term debt	2,961	3,211
Common Stock, Value, Issued	0	0
Additional paid in capital	3,370	3,311
Retained earnings	617	540
Accumulated other comprehensive loss	(1)	(1)
Total common stockholder's equity	3,986	3,850
Total liabilities and equity	9,881	9,748
Affiliated Entity
Current assets
Accounts receivable, net	222	167
Current liabilities
Accounts payable	188	209
Related Party
Current assets
Accounts receivable, net	26	15
Current liabilities
Accounts payable	$ 7	$ 23

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Common Stock, Shares Authorized	200	200
Common Stock, Par or Stated Value Per Share	$ 1	$ 1
Common Stock, Shares, Outstanding	100	100

STATEMENTS OF COMMON STOCKHOLDE

STATEMENTS OF COMMON STOCKHOLDER'S EQUITY - USD ($) $ in Millions	Total	Common stock	Additional Paid In Capital	Retained Earnings	AOCI Attributable to Parent
Beginning Balance (in shares) at Dec. 31, 2020		100
Beginning Balance at Dec. 31, 2020	$ 3,298	$ 0	$ 2,790	$ 509	$ (1)
Increase (Decrease) in Stockholder's Equity
Net Income (Loss) Attributable to Parent	318			318
Common dividends declared to parent	(314)			(314)
Contribution of capital by parent	301		301
Ending Balance (in shares) at Dec. 31, 2021		100
Ending Balance at Dec. 31, 2021	3,603	$ 0	3,091	513	(1)
Increase (Decrease) in Stockholder's Equity
Net Income (Loss) Attributable to Parent	349			349
Common dividends declared to parent	(322)			(322)
Contribution of capital by parent	$ 220		220
Ending Balance (in shares) at Dec. 31, 2022	100	100
Ending Balance at Dec. 31, 2022	$ 3,850	$ 0	3,311	540	(1)
Increase (Decrease) in Stockholder's Equity
Net Income (Loss) Attributable to Parent	384			384
Common dividends declared to parent	(307)			(307)
Contribution of capital by parent	$ 59		59
Ending Balance (in shares) at Dec. 31, 2023	100	100
Ending Balance at Dec. 31, 2023	$ 3,986	$ 0	$ 3,370	$ 617	$ (1)

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Legal SPS is involved in various litigation matters 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 a series of complex judgments about future events. Management maintains accruals for losses 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 but not limited to 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, including a possible eventual loss. For current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, would have a material effect on SPS’ financial statements. Legal fees are generally expensed as incurred. Rate Matters SPS is involved in various regulatory proceedings arising in the ordinary course of business. Until resolution, typically in the form of a rate order, uncertainties may exist regarding the ultimate rate treatment for certain activities and transactions. Amounts have been recognized for probable and reasonably estimable losses that may result. Unless otherwise disclosed, any reasonably possible range of loss in excess of any recognized amount is not expected to have a material effect on the financial statements. SPP OATT Upgrade Costs — Costs of transmission upgrades may be recovered from other SPP customers whose transmission service depends on capacity enabled by the upgrade under the SPP OATT. 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 2018, SPS’ appeal to the D.C. Circuit over the FERC rulings granting SPP the right to recover previously unbilled charges was remanded to the FERC. In 2019, the FERC reversed its 2016 decision and ordered SPP to refund charges retroactively collected from its transmission customers, including SPS, related to periods before September 2015. In 2020, SPP and Oklahoma Gas & Electric separately filed petitions for review of the FERC’s orders at the D.C. Circuit. In 2021, the D.C. Circuit issued a decision denying these appeals and upholding the FERC’s orders. Refunds received by SPS are expected to be given back to SPS customers through future rates. Wind Operating Commitments Environmental New and changing federal and state environmental mandates can create financial liabilities for SPS, which are normally recovered through the regulated rate process. Site Remediation Various federal and state environmental laws impose liability where hazardous substances or other regulated materials have been released to the environment. SPS may sometimes pay all or a portion of the cost to remediate sites where past activities of SPS’ predecessors or other parties have caused environmental contamination. Environmental contingencies could arise from various situations, including sites of former MGPs; and third-party sites, such as landfills, for which SPS is alleged to have sent wastes to that site. MGP, Landfill and Disposal Sites SPS is investigating, remediating or performing post-closure actions at two MGP, landfill or other disposal sites across its service territories, excluding sites that are being addressed under coal ash regulations. SPS has recognized its best estimate of costs/liabilities from final resolution of these issues, however, the outcome and timing are unknown. In addition, there may be insurance recovery and/or recovery from other potentially responsible parties, offsetting a portion of costs incurred. Environmental Requirements — Air Clean Air Act NOx Allowance Allocations — In June 2023, the EPA published final regulations under the "Good Neighbor" provisions of the Clean Air Act. The final rule applies to generation facilities in Texas, as well as other states outside of our service territory. The rule establishes an allowance trading program for NOx that will impact SPS’ fossil fuel-fired electric generating facilities. Applicable facilities will have to secure additional allowances, install NOx controls and/or develop a strategy of operations that utilizes the existing allowance allocations. Guidelines are also established for allowance banking and emission limit backstops. While the financial impacts of the final rule are uncertain and dependent on market forces and anticipated generation, SPS anticipates the annual costs could be significant, but would be recoverable through regulatory mechanisms. SPS has joined other companies in litigation challenging the EPA’s disapproval of Texas’ state implementation plan. Currently, the regulation is under a judicial stay for Texas and not applicable in that jurisdiction until litigation concludes. In February 2024, the EPA proposed to partially disapprove New Mexico’s state implementation plan and bring New Mexico into the federal Good Neighbor plan. Xcel Energy continues to evaluate impacts to generation units at SPS. AROs — AROs have been recorded for SPS’ assets, as follows: 2023 (Millions of Dollars) Jan. 1, 2023 Accretion Dec. 31, 2023 Electric Steam and other production $ 83 $ 4 $ 87 Wind 54 2 56 Distribution 10 — 10 Total liability $ 147 $ 6 $ 153 2022 (Millions of Dollars) Jan. 1, 2022 Accretion Cash Flow Revisions (a) Dec. 31, 2022 Electric Steam and other production $ 54 $ 3 $ 26 $ 83 Wind 52 2 — 54 Distribution 10 — — 10 Total liability $ 116 $ 5 $ 26 $ 147 (a) In 2022, AROs were revised for changes in estimates of cash flows. Revisions in steam and other production AROs primarily related to changes in costs for steam production ponds remediation. Indeterminate AROs — Outside of the recorded asbestos AROs, other plants or buildings may contain asbestos due to the age of many of SPS’ facilities, but no confirmation or measurement of the cost of removal could be determined as of Dec. 31, 2023. Therefore, an ARO has not been recorded for these facilities. Leases SPS evaluates contracts that may contain leases, including PPAs and arrangements for the use of office space and other facilities, vehicles and equipment. 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. The present value of future operating lease payments is recognized in current 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. Therefore, the present value of future lease payments is generally calculated using the estimated incremental borrowing rate (weighted average of 4.4%). For currently existing asset classes, SPS has elected to utilize the practical expedient under which non-lease components, such as asset maintenance costs included in payments, 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) Dec. 31, 2023 Dec. 31, 2022 PPAs $ 500 $ 500 Other 44 44 Gross operating lease ROU assets 544 544 Accumulated amortization (141) (110) Net operating lease ROU assets $ 403 $ 434 Components of lease expense: (Millions of Dollars) 2023 2022 2021 Operating leases PPA capacity payments $ 53 $ 53 $ 53 Other operating leases (a) 4 4 4 Total operating lease expense (b) $ 57 $ 57 $ 57 (a) Includes immaterial short-term lease expense for 2023, 2022 and 2021. (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. Commitments under operating leases as of Dec. 31, 2023: (Millions of Dollars) PPA (a) (b) Operating Leases Other Operating Leases Total Leases 2024 $ 46 $ 3 $ 49 2025 46 3 49 2026 46 3 49 2027 46 4 50 2028 46 4 50 Thereafter 220 33 253 Total minimum obligation 450 50 500 Interest component of obligation (85) (12) (97) Present value of minimum obligation 365 38 403 Less current portion (32) Noncurrent operating and finance lease liabilities $ 371 Weighted-average remaining lease term in years 10 (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. Non-Lease PPAs — SPS has entered into PPAs with other utilities and energy suppliers for purchased power to meet system load and energy requirements, operating reserve obligations and as part of wholesale and commodity trading activities. In general, these agreements provide for energy payments, based on actual energy delivered and capacity payments. Certain PPAs, accounted for as executory contracts with various expiration dates through 2026, contain minimum energy purchase requirements. Total energy payments on those contracts were $29 million in 2023. Included in electric fuel and purchased power expenses for PPAs accounted for as executory contracts, were payments for capacity of $12 million in 2023, 2022 and 2021. Capacity and energy payments are contingent on the IPPs meeting contract obligations, including plant availability requirements. Certain contractual payments are adjusted based on market indices. At Dec. 31, 2023, the estimated future payments for capacity and energy that SPS is obligated to purchase pursuant to these executory contracts, subject to availability, were as follows: (Millions of Dollars) Capacity Energy (a) 2024 $ 14 $ 33 2025 16 40 2026 16 38 2027 — — 2028 — — Thereafter — — Total $ 46 $ 111 (a) Excludes contingent energy payments for renewable energy PPAs. Amounts exclude approximately $1 billion of minimum payments related to SPS’ extension of a non-lease PPA that otherwise expires in 2026, pending PUCT and NMPRC approvals to extend the agreement to 2039. Approval processes are expected to conclude in 2024. Fuel Contracts — SPS has entered into various long-term commitments for the purchase and delivery of a significant portion of its coal and natural gas requirements. These contracts expire between 2024 and 2033. SPS is required to pay additional amounts depending on actual quantities shipped under these agreements. Estimated minimum purchases under these contracts as of Dec. 31, 2023: (Millions of Dollars) Coal Natural gas Natural gas 2024 $ 86 $ 21 $ 33 2025 20 — 29 2026 20 — 24 2027 20 — 24 2028 20 — 17 Thereafter — — 6 Total $ 166 $ 21 $ 133 VIEs PPAs — 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. SPS has determined that certain IPPs are VIEs. SPS is not subject to risk of loss from the operations of these entities, and no significant financial support is required other than contractual payments for energy and capacity. In addition, certain solar PPAs provide an option to purchase emission allowances or sharing provisions related to production credits generated by the solar facility under contract. These specific PPAs create a variable interest in the IPP. SPS evaluated each of these VIEs for possible consolidation, including review of qualitative factors such as the length and terms of the contract, control over O&M, control over dispatch of electricity, historical and estimated future fuel and electricity prices, and financing activities. 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. SPS had approximately 1,197 MW of capacity under long-term PPAs at both Dec. 31, 2023 and 2022 with entities that have been determined to be VIEs. These agreements have expiration dates through 2041. Fuel Contracts — SPS purchases all of its coal requirements for its Harrington and Tolk plants from TUCO Inc. under contracts that will expire in December 2024 and December 2027, respectively. TUCO arranges for the purchase, receiving, transporting, unloading, handling, crushing, weighing, and delivery of coal to meet SPS’ requirements. TUCO is responsible for negotiating and administering contracts with coal suppliers, transporters and handlers. SPS has not provided any significant financial support to TUCO, other than contractual payments for delivered coal. However, the fuel contracts create a variable interest in TUCO due to SPS’ reimbursement of fuel procurement costs. SPS has determined that TUCO is a VIE, however it has concluded that SPS is not the primary beneficiary because it does not have the power to direct the activities that most significantly impact TUCO’s economic performance.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Significant Accounting Policies	General — SPS is engaged in the regulated generation, purchase, transmission, distribution and sale of electricity. SPS’ financial statements are presented in accordance with GAAP. All of SPS’ underlying accounting records also conform to the FERC uniform system of accounts or to systems required by various state regulatory commissions. Certain amounts in the financial statements or notes have been reclassified for comparative purposes; however, such reclassifications did not affect net income, total assets, liabilities, equity or cash flows. SPS has evaluated events occurring after Dec. 31, 2023 up to the date of issuance of these financial statements. These statements contain all necessary adjustments and disclosures resulting from that evaluation. Use of Estimates — SPS uses estimates based on the best information available to record transactions and balances resulting from business operations. Estimates are used for items such as plant depreciable lives or potential disallowances, AROs, certain regulatory assets and liabilities, tax provisions, uncollectible amounts, environmental costs, unbilled revenues, jurisdictional fuel and energy cost allocations and actuarially determined benefit costs. Recorded estimates are revised when better information becomes available or actual amounts can be determined. Revisions can affect operating results. Regulatory Accounting — SPS accounts for income and expense items in accordance with accounting guidance for regulated operations. Under this guidance: • Certain costs, which would otherwise be charged to expense or other comprehensive income, are deferred as regulatory assets based on the expected ability to recover the costs in future rates. • Certain credits, which would otherwise be reflected as income or other comprehensive income, are deferred as regulatory liabilities based on the expectation the amounts will be returned to customers in future rates or because the amounts were collected in rates prior to the costs being incurred. Estimates and assumptions for recovery of deferred costs and refund of deferred credits are based on specific ratemaking decisions, precedent or other available information. Regulatory assets and liabilities are amortized consistent with the treatment in the rate setting process. If changes in the regulatory environment occur, SPS may no longer be eligible to apply this accounting treatment and may be required to eliminate regulatory assets and liabilities. Such changes could have a material effect on SPS’ results of operations, financial condition and cash flows. See Note 4 for further information. Income Taxes — SPS accounts for income taxes using the asset and liability method, which requires recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Income taxes are deferred for all temporary differences between pretax financial and taxable income and between the book and tax bases of assets and liabilities utilizing rates that are scheduled to be in effect when the temporary differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the period that includes the enactment date. Utility rate regulation has resulted in the recognition of regulatory assets and liabilities related to income taxes. The effects of SPS’ tax rate changes are generally subject to a normalization method of accounting. Therefore, the revaluation of most of its net deferred taxes upon a tax rate reduction results in the establishment of a net regulatory liability, refundable to utility customers over the remaining life of the related assets. SPS anticipates that a tax rate increase would predominantly result in the establishment of a regulatory asset, subject to an evaluation of whether future recovery is expected. Tax credits are recorded when earned unless there is a requirement to defer the benefit and amortize over the book depreciable lives of related property. The requirement to defer and amortize these credits specifically applies to certain federal ITCs, as determined by tax regulations and SPS tax elections. For tax credits otherwise eligible to be recognized when earned, SPS considers the impact of rate regulation to determine if these credits and related adjustments should be deferred as regulatory assets or liabilities. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that some portion or all of the deferred tax asset will not be realized. This evaluation includes consideration of whether tax credits are expected to be sold at a discount and impact the realization of amounts presented as deferred tax assets. Transferable tax credits are accounted for under ASC 740 Income Taxes , and valuation allowances and any adjustments for discounts incurred on sales transactions are recorded to deferred tax expense. SPS measures and discloses uncertain tax positions that it has taken or expects to take in its income tax returns. A tax position is recognized in the financial statements when it is more likely than not that the position will be sustained upon examination based on the technical merits of the position. Recognition of changes in uncertain tax positions are reflected as a component of income tax expense. Interest and penalties related to income taxes are reported within Other income, net or interest charges in the statements of income. Xcel Energy Inc. and its subsidiaries, including SPS file consolidated federal income tax returns as well as consolidated or separate state income tax returns. Federal income taxes paid by Xcel Energy Inc. are allocated to its subsidiaries based on separate company computations. A similar allocation is made for state income taxes paid by Xcel Energy Inc. in connection with consolidated state filings. Xcel Energy Inc. also allocates its own income tax benefits to its direct subsidiaries. See Note 7 for further information. Property, Plant and Equipment and Depreciation in Regulated Operations — Property, plant and equipment is stated at original cost. The cost of plant includes direct labor and materials, contracted work, overhead costs and AFUDC. The cost of plant retired is charged to accumulated depreciation and amortization. Amounts recovered in rates for future removal costs are recorded as regulatory liabilities. Significant additions or improvements extending asset lives are capitalized, while repairs and maintenance costs and replacement of items determined to be less than a unit of property are charged to expense as incurred. Property, plant and equipment is tested for impairment when it is determined that the carrying value of the assets may not be recoverable. A loss is recognized in the current period if it becomes probable that part of a cost of a plant under construction or recently completed plant will be disallowed for recovery from customers and a reasonable estimate of the disallowance can be made. For investments in property, plant and equipment that are abandoned and not expected to go into service, incurred costs and related deferred tax amounts are compared to the discounted estimated future rate recovery, and a loss is recognized, if necessary. Depreciation expense is recorded using the straight-line method over the plant’s commission approved useful life. Actuarial life studies are performed and submitted to the state and federal commissions for review. Upon acceptance by the various commissions, the resulting lives and net salvage rates are used to calculate depreciation. Plant removal costs are typically recognized at the amounts recovered in rates as authorized by the applicable regulator. Accumulated removal costs are reflected in the balance sheet as a regulatory liability. Depreciation expense, expressed as a percentage of average depreciable property, was 3.4% in 2023, 3.4% in 2022 and 3.3% in 2021. See Note 3 for further information. AROs — SPS records AROs as a liability in the period incurred (if fair value can be reasonably estimated), with the offsetting/associated costs capitalized as a long-lived asset. The liability is generally increased over time by applying the effective interest method of accretion and the capitalized costs are typically depreciated over the useful life of the long-lived asset. Changes resulting from revisions to timing or amounts of expected asset retirement cash flows are recognized as an increase or a decrease in the ARO. See Note 10 for further information. Benefit Plans and Other Postretirement Benefits — SPS maintains pension and postretirement benefit plans for eligible employees. Recognizing the cost of providing benefits and measuring the projected benefit obligation of these plans requires management to make various assumptions and estimates. Certain unrecognized actuarial gains and losses and unrecognized prior service costs or credits are deferred as regulatory assets and liabilities, rather than recorded as other comprehensive income, based on regulatory recovery mechanisms. See Note 9 for further information. Environmental Costs — Environmental costs are recorded when it is probable SPS is liable for remediation costs and the amount can be reasonably estimated. Costs are deferred as a regulatory asset if it is probable the costs will be recovered from customers in future rates. Otherwise, the costs are expensed. For certain environmental costs related to facilities currently in use, such as for emission-control equipment, the cost is capitalized and depreciated over the life of the plant. Estimated remediation costs are regularly adjusted as estimates are revised and remediation is performed. If other participating potentially responsible parties exist and acknowledge their potential involvement with a site, costs are estimated and recorded only for SPS’ expected share of the cost. Estimated future expenditures to restore sites are treated as a capitalized cost of plant retirement. The depreciation expense levels recoverable in rates include a provision for removal expenses. Removal costs recovered in rates before the related costs are incurred are classified as a regulatory liability. See Note 10 for further information. Revenue from Contracts with Customers — Performance obligations related to the sale of energy are satisfied as energy is delivered to customers. SPS recognizes revenue that corresponds to the price of the energy delivered to the customer. The measurement of energy sales to customers is generally based on the reading of their meters, which occurs systematically throughout the month. At the end of each month, amounts of energy delivered to customers since the date of the last meter reading are estimated and the corresponding unbilled revenue is recognized. A separate financing component of collections from customers is not recognized as contract terms are short-term in nature. Revenues are net of any excise or sales taxes or fees. SPS participates in SPP. SPS recognizes physical sales to customers (native load and wholesale) on a gross basis in electric revenues and cost of sales. Revenues and charges for short-term physical wholesale sales of excess energy transacted through RTOs are also recorded on a gross basis. Other revenues and charges settled/facilitated through an RTO are recorded on a net basis in cost of sales. See Note 6 for further information. Cash and Cash Equivalents — SPS considers investments in instruments with a remaining maturity of 3 months or less at the time of purchase to be cash equivalents. Accounts Receivable and Allowance for Bad Debts — Accounts receivable are stated at the actual billed amount net of an allowance for bad debts. SPS establishes an allowance for uncollectible receivables based on a policy that reflects its expected exposure to the credit risk of customers. As of Dec. 31, 2023 and 2022, the allowance for bad debts was $15 million and $13 million, respectively. Inventory — Inventory is recorded at the lower of average cost or net realizable value and consisted of the following: (Millions of Dollars) Dec. 31, 2023 Dec. 31, 2022 Inventories Materials and supplies $ 56 $ 42 Fuel 13 19 Total inventories $ 69 $ 61 Fair Value Measurements — SPS presents cash equivalents, interest rate derivatives and commodity derivatives at estimated fair values in its financial statements. For interest rate derivatives, quoted prices based primarily on observable market interest rate curves are used to estimate fair value. For commodity derivatives, the most observable inputs available are generally used to determine the fair value of each contract. In the absence of a quoted price, quoted prices for similar contracts or internally prepared valuation models may be used to determine fair value. For the pension and postretirement plan assets and nuclear decommissioning fund, published trading data and pricing models, generally using the most observable inputs available, are utilized to determine fair value for each security. See Notes 8 and 9 for further information. Derivative Instruments — SPS uses derivative instruments in connection with its commodity trading activities, and to manage risk associated with changes in interest rates and utility commodity prices, including forward contracts, futures, swaps and options. Derivatives not qualifying for the normal purchases and normal sales exception are recorded on the balance sheets at fair value as derivative instruments. Classification of changes in fair value for those derivative instruments is dependent on the designation of a qualifying hedging relationship. Changes in fair value of derivative instruments not designated in a qualifying hedging relationship are reflected in current earnings or as a regulatory asset or liability. Classification as a regulatory asset or liability is based on commission approved regulatory recovery mechanisms. Gains or losses on commodity trading transactions are recorded as a component of electric operating revenues. Normal Purchases and Normal Sales — SPS enters into contracts for purchases and sales of commodities for use in its operations. At inception, contracts are evaluated to determine whether they contain a derivative, and if so, whether they may be exempted from derivative accounting if designated as normal purchases or normal sales. See Note 8 for further information. Other Utility Items AFUDC — AFUDC represents the cost of capital used to finance utility construction activity and is computed by applying a composite financing rate to qualified CWIP. The amount of AFUDC capitalized as a utility construction cost is credited to other nonoperating income (for equity capital) and interest charges (for debt capital). AFUDC amounts capitalized are included in SPS’ rate base. Alternative Revenue — Certain rate rider mechanisms (including DSM programs) qualify as alternative revenue programs. These mechanisms arise from instances in which the regulator authorizes a future surcharge in response to past activities or completed events. When certain criteria are met, including expected collection within 24 months, revenue is recognized equal to the revenue requirement, which may include incentives and return on rate base items. Billing amounts are revised periodically for differences between total amount collected and revenue earned, which may increase or decrease the level of revenue collected from customers. Alternative revenues arising from these programs are presented on a gross basis and disclosed separately from revenue from contracts with customers. See Note 6 for further information. Conservation Programs — SPS has implemented programs in its jurisdictions to assist customers in conserving energy and reducing peak demand on the electric system. These programs include commercial motor, air conditioner and lighting upgrades, as well as residential rebates for participation in air conditioner interruption and home weatherization. The costs incurred for some DSM programs are deferred as permitted by the applicable regulatory jurisdiction. For those programs, costs are deferred if it is probable future revenue will be provided to permit recovery of the incurred cost. Revenues recognized for incentive programs designed for recovery of lost margins and/or conservation performance incentives are limited to amounts expected to be collected within 24 months from the annual period in which they are earned. SPS recovers approved conservation program costs in base rate revenue or through a rider. Emissions Allowances — Emissions allowances are recorded at cost, including broker commission fees. The inventory accounting model is utilized for all emission allowances and sales of these allowances are included in electric revenues. RECs — Cost of RECs that are utilized for compliance is recorded as electric fuel and purchased power expense. SPS reduces recoverable fuel and purchased power costs for the cost of RECs received. An inventory accounting model is used to account for RECs, however these assets are classified as regulatory assets if amounts are recoverable in future rates. Segment Information

Property Plant and Equipment Pr

Property Plant and Equipment Property Plant and Equipment	12 Months Ended
	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment Disclosure	Major classes of property, plant and equipment (Millions of Dollars) Dec. 31, 2023 Dec. 31, 2022 Property, plant and equipment, net Electric plant $ 10,752 $ 10,182 Plant to be retired (a) 248 266 CWIP 226 167 Total property, plant and equipment 11,226 10,615 Less accumulated depreciation (2,690) (2,486) Property, plant and equipment, net $ 8,536 $ 8,129 (a) Amounts include Tolk Unit 1 and 2 and coal generation assets at Harrington pending facility gas conversion. Amounts are reported net of accumulated depreciation.

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities	12 Months Ended
	Dec. 31, 2023
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Regulatory assets and liabilities are created for amounts that regulators may allow to be collected or may require to be paid back to customers in future electric rates. SPS would be required to recognize the write-off of regulatory assets and liabilities in net income or other comprehensive income if changes in the utility industry no longer allow for the application of regulatory accounting guidance under GAAP. Components of regulatory assets: (Millions of Dollars) See Note(s) Remaining Amortization Period Dec. 31, 2023 Dec. 31, 2022 (a) Regulatory Assets Current Noncurrent Current Noncurrent Pension and retiree medical obligations 9 Various $ 2 $ 147 $ 2 $ 146 Net AROs (b) 1, 10 Various — 59 — 48 Excess deferred taxes — TCJA 7 Various 1 47 1 48 Recoverable deferred taxes on AFUDC Plant lives — 44 — 40 Losses on reacquired debt Term of related debt 1 18 1 19 Deferred electric energy/fuel costs N/A — — 136 34 Other Various 26 34 77 24 Total regulatory assets $ 30 $ 349 $ 217 $ 359 (a) Prior period amounts have been restated to conform with current year presentation. (b) Includes amounts recorded for future recovery of AROs. Components of regulatory liabilities: (Millions of Dollars) See Note(s) Remaining Amortization Period Dec. 31, 2023 Dec. 31, 2022 (a) Regulatory Liabilities Current Noncurrent Current Noncurrent Deferred income tax adjustments and TCJA refunds (b) 7 Various $ — $ 458 $ — $ 469 Plant removal costs 1, 10 Various — 223 — 198 LP&L departure payment Up to 10 years 33 33 — — Effects of regulation on employee benefit costs Various — 19 — 20 Formula rates One two 13 10 10 8 Renewable resources and environmental initiatives Various — 8 — 14 Contract valuation adjustments (c) 1, 8 Less than one 41 — 119 1 Deferred electric energy costs Less than one 15 — — — Other Various 14 10 19 5 Total regulatory liabilities $ 116 $ 761 $ 148 $ 715 (a) Prior period amounts have been reclassified to conform with current year presentation. (b) Includes the revaluation of recoverable/regulated plant accumulated deferred income taxes and revaluation impact of non-plant accumulated deferred income taxes due to the TCJA. (c) Includes the fair value of FTR instruments utilized/intended to offset the impacts of transmission system congestion.

Borrowings and Other Financing

Borrowings and Other Financing Instruments	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Borrowings and Other Financing Instruments	5. 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: (Millions of Dollars, Except Interest Rates) Three Months Ended Dec. 31, 2023 Year Ended Dec. 31 2023 2022 2021 Borrowing limit $ 100 $ 100 $ 100 $ 100 Amount outstanding at period end 27 27 — 91 Average amount outstanding 14 46 35 51 Maximum amount outstanding 44 100 100 100 Weighted average interest rate, computed on a daily basis 5.34 % 5.04 % 0.44 % 0.05 % Weighted average interest rate at end of period 5.34 5.34 N/A 0.05 Commercial Paper — Commercial paper outstanding: (Millions of Dollars, Except Interest Rates) Three Months Ended Dec. 31, 2023 Year Ended Dec. 31 2023 2022 2021 Borrowing limit $ 500 $ 500 $ 500 $ 500 Amount outstanding at period end 75 75 34 137 Average amount outstanding 18 50 100 63 Maximum amount outstanding 95 119 324 342 Weighted average interest rate, computed on a daily basis 5.54 % 5.12 % 0.79 % 0.21 % Weighted average interest rate at end of period 5.56 5.56 4.55 0.26 Letters of Credit — SPS may use letters of credit, typically with terms of one year, to provide financial guarantees for certain operating obligations. At Dec. 31, 2023 and 2022, there were $0 and $2 million of letters of credit outstanding under the credit facility, respectively. 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. Features of SPS’ credit facility: Debt-to-Total Capitalization Ratio (a) Amount Facility May Be Increased (millions of dollars) Additional Periods for Which a One-Year Extension May Be Requested (b) 2023 2022 46.1% 45.7% $50 2 (a) The credit facility has a financial covenant requiring that the debt-to-total capitalization ratio be less than or equal to 65%. (b) All extension requests are subject to majority bank group approval. The credit facility has a cross-default provision that SPS would be in default on its borrowings under the facility if SPS or any of its future significant subsidiaries whose total assets exceed 15% of SPS’ total assets default on indebtedness in an aggregate principal amount exceeding $75 million. If SPS does not comply with the covenant, an event of default may be declared, and if not remedied, any outstanding amounts due under the facility can be declared due by the lender. As of Dec. 31, 2023, SPS was in compliance with all financial covenants. SPS had the following committed credit facility available as of Dec. 31, 2023 (in millions) of dollars: Credit Facility (a) Drawn (b) Available $ 500 $ 75 $ 425 (a) This credit facility matures in September 2027. (b) Includes letters of credit and outstanding commercial paper. 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 facility outstanding at Dec. 31, 2023 and 2022. Long-Term Borrowings and Other Financing Instruments Generally, the property of SPS is subject to the lien of its first mortgage indenture for the benefit of bondholders. Debt premiums, discounts and expenses are amortized over the life of the related debt. The premiums, discounts and expenses for refinanced debt are deferred and amortized over the life of the new issuance. Long-term debt obligations for SPS as of Dec. 31 (in millions of dollars): Financing Instrument Interest Rate Maturity Date 2023 2022 First mortgage bonds 3.30 % June 15, 2024 $ 150 $ 150 First mortgage bonds 3.30 June 15, 2024 200 200 Unsecured senior notes 6.00 Oct. 1, 2033 100 100 Unsecured senior notes 6.00 Oct. 1, 2036 250 250 First mortgage bonds 4.50 Aug. 15, 2041 200 200 First mortgage bonds 4.50 Aug. 15, 2041 100 100 First mortgage bonds 4.50 Aug. 15, 2041 100 100 First mortgage bonds 3.40 Aug. 15, 2046 300 300 First mortgage bonds 3.70 Aug. 15, 2047 450 450 First mortgage bonds 4.40 Nov. 15, 2048 300 300 First mortgage bonds 3.75 June 15, 2049 300 300 First mortgage bonds 3.15 May 1, 2050 350 350 First mortgage bonds 3.15 May 1, 2050 250 250 First mortgage bonds (a) 5.15 June 1, 2052 200 200 First mortgage bonds (b) 6.00 Sept. 15, 2053 100 — Unamortized discount (10) (10) Unamortized debt issuance cost (29) (29) Current maturities (350) — Total long-term debt $ 2,961 $ 3,211 (a) 2022 financing. (b) 2023 financing. Maturities of long-term debt: (Millions of Dollars) 2024 $ 350 2025 — 2026 — 2027 — 2028 — Deferred Financing Costs — Deferred financing costs of approximately $29 million, net of amortization, are presented as a deduction from the carrying amount of long-term debt at Dec. 31, 2023 and 2022, respectively. Capital Stock — SPS has the following preferred stock: Preferred Stock Authorized (Shares) Par Value of Preferred Stock Preferred Stock Outstanding (Shares) 2023 and 2022 10,000,000 1.00 — Dividend Restrictions — SPS dividends are subject to the FERC’s jurisdiction, which prohibits the payment of dividends out of capital accounts. Dividends are solely to be paid from retained earnings. SPS is required to be current on particular interest payments before dividends can be paid. SPS’ state regulatory commissions additionally impose dividend limitations, which are more restrictive than those imposed by the FERC. Requirements and actuals as of Dec. 31, 2023: Equity to Total Capitalization Ratio Equity to Total Capitalization Ratio Actual (a) Low High 2023 45.0 % 55.0 % 54.6 % (a) Excludes short-term debt. Unrestricted Retained Earnings Total Capitalization Limit on Total Capitalization (a) $ 617 million $ 7,298 million N/A (a)

Revenues

Revenues	12 Months Ended
	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Revenues	Revenue is classified by the type of goods/services rendered and market/customer type. SPS’ operating revenues consisted of the following: Year Ended Dec. 31 (Millions of Dollars) 2023 2022 2021 Major revenue types Revenue from contracts with customers: Residential $ 442 $ 445 $ 375 C&I (a) 1,094 1,102 842 Other 58 51 38 Total retail 1,594 1,598 1,255 Wholesale 223 407 873 Transmission 296 296 287 Other — 10 6 Total revenue from contracts with customers 2,113 2,311 2,421 Alternative revenue and other 39 115 44 Total revenues $ 2,152 $ 2,426 $ 2,465

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	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. Effective income tax rate for years ended Dec. 31: 2023 2022 2021 Federal statutory rate 21.0 % 21.0 % 21.0 % State income tax on pretax income, net of federal tax effect 2.4 2.3 2.5 Increases (decreases) in tax from: Wind PTCs (a) (33.5) (35.9) (39.7) Plant regulatory differences (b) (3.3) (3.8) (4.8) Amortization of deficient/(excess) nonplant deferred taxes 0.3 (0.9) (1.1) Other, net (0.2) (0.6) (0.7) Effective income tax rate (13.3) % (17.9) % (22.8) % (a) Wind PTCs net of estimated transfer discounts. Gross wind PTCs are credited to customers (reduction to revenue) and do not materially impact net income. (b) Plant regulatory differences primarily relate to the credit of excess deferred taxes to customers through the average rate assumption method. Income tax benefits associated with the credit are offset by corresponding revenue reductions. Components of income tax expense for years ended Dec. 31: (Millions of Dollars) 2023 2022 2021 Current federal tax expense (benefit) $ 76 $ (65) $ (11) Current state tax expense (benefit) 12 (5) (1) Deferred federal tax (benefit) expense (132) 3 (57) Deferred state tax (benefit) expense (1) 13 9 Deferred change in unrecognized tax expense — 1 1 Total income tax benefit $ (45) $ (53) $ (59) Components of deferred income tax expense as of Dec. 31: (Millions of Dollars) 2023 2022 2021 Deferred tax (benefit) expense excluding items below $ (117) $ 37 $ (23) Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities (16) (20) (24) Deferred tax (benefit) expense $ (133) $ 17 $ (47) Components of the net deferred tax liability as of Dec. 31: (Millions of Dollars) 2023 2022 (a) Deferred tax liabilities: Differences between book and tax bases of property $ 1,072 $ 1,015 Operating lease assets 90 97 Regulatory assets 51 61 Pension expense 32 33 Total deferred tax liabilities $ 1,245 $ 1,206 Deferred tax assets: Tax credit carryforward $ 406 $ 294 Regulatory liabilities 95 98 Operating lease liabilities 90 97 Other employee benefits 6 6 Deferred fuel costs 5 (35) NOL carryforward — 2 Tax credit valuation allowances (2) — Other 23 5 Total deferred tax assets 623 467 Net deferred tax liability $ 622 $ 739 (a) Prior periods have been reclassified to conform to current year presentation. Other Income Tax Matters — NOL amounts represent the tax loss that is carried forward and tax credits represent the deferred tax asset. NOL and tax credit carryforwards as of Dec. 31 were as follows: (Millions of Dollars) 2023 2022 Federal NOL carryforward $ — $ 8 Federal tax credit carryforwards 406 294 Valuation allowances for federal credit carryforwards (2) — State NOL carryforwards 3 4 Federal carryforward periods expire between 2038 and 2043 and state carryforward periods expire starting 2034. Unrecognized Tax Benefits Federal Audit — SPS is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. The statute of limitations applicable to Xcel Energy’s consolidated federal tax returns expire as follows: Tax Year(s) Expiration 2014 - 2016 March 2025 2020 September 2024 Additionally, the statute of limitations related to the federal tax credit carryforwards will remain open until those credits are utilized in subsequent returns. Further, the statute of limitations related to the additional federal tax loss carryback claim filed in 2020 has been extended. As of Dec. 31, 2023 the IRS issued its Revenue Agent’s Report related to the federal tax loss carryback claim. The Company materially agrees with the report and re-recognized the related benefit in Dec. 2023. State Audits — SPS is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of Dec. 31, 2023, SPS’ earliest open tax years that are subject to examination by state taxing authorities under applicable statutes of limitations are as follows: State Tax Year(s) Expiration Texas 2016, 2018 May 2024 Texas 2017 July 2025 Texas 2019 August 2024 In 2021, Texas began an audit of tax years 2016 - 2019. As of Dec. 31, 2023, no material adjustments have been proposed. Unrecognized tax benefit balance includes permanent tax positions, which if recognized would affect the ETR. In addition, the unrecognized tax benefit balance includes temporary tax positions for which deductibility is highly certain, but for which there is uncertainty about the timing. A change in the timing of deductibility would not affect the ETR but would accelerate the payment to the taxing authority. Unrecognized tax benefits — permanent vs temporary: (Millions of Dollars) Dec. 31, 2023 Dec. 31, 2022 Unrecognized tax benefit — Permanent tax positions $ 5 $ 5 Unrecognized tax benefit — Temporary tax positions — 4 Total unrecognized tax benefit $ 5 $ 9 Changes in unrecognized tax benefits: (Millions of Dollars) 2023 2022 2021 Balance at Jan. 1 $ 9 $ 8 $ 7 Additions based on tax positions related to the current year 1 1 1 Reductions for tax positions of prior years (5) — — Balance at Dec. 31 $ 5 $ 9 $ 8 Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards: (Millions of Dollars) Dec. 31, 2023 Dec. 31, 2022 NOL and tax credit carryforwards $ (4) $ (8) As IRS audits resume and state audits progress, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $2 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) 2023 2022 2021 Payable for interest related to unrecognized tax benefits at Jan. 1 $ — $ (1) $ (1) Interest expense related to unrecognized tax benefits — 1 — Payable for interest related to unrecognized tax benefits at Dec. 31 $ — $ — $ (1) No amounts were accrued for penalties related to unrecognized tax benefits as of Dec. 31, 2023, 2022 or 2021.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	Fair Value Measurements Accounting guidance for fair value measurements and disclosures provides a hierarchical framework for disclosing the observability of the inputs utilized in measuring assets and liabilities at fair value. • 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 actively traded instruments with observable actual trading prices. • Level 2 — Pricing inputs are other than actual trading 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 include those valued with models requiring significant judgment or estimation. Specific valuation methods include: Interest rate derivatives — Fair values of interest rate derivatives are based on broker quotes that utilize current market interest rate forecasts. Commodity derivatives — Methods used to measure the fair value of commodity derivative forwards and options utilize forward prices and volatilities, as well as pricing adjustments for specific delivery locations, and are generally assigned a Level 2 classification. When contracts relate to inactive delivery locations or extend to periods beyond those readily observable on active exchanges, 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. 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 values of these instruments are derived from, and designed to offset, the costs 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 these instruments. FTRs are recognized at fair value and adjusted each period prior to settlement. Given the limited observability of certain variables underlying the reported auction, values of FTRs, these fair value measurements have been assigned a Level 3 classification. Net congestion costs, including the impact of FTR settlements, are shared through fuel and purchased energy cost recovery mechanisms. As such, the fair value of the unsettled instruments (i.e., derivative asset or liability) is offset/deferred as a regulatory asset or liability. Derivative Activities and 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 utility commodity prices. Interest Rate Derivatives — SPS enters into contracts that effectively fix the interest rate on a specified principal amount of a hypothetical future debt issuance. These financial swaps net settle based on changes in a specified benchmark interest rate, acting as a hedge of changes in market interest rates that will impact specified anticipated debt issuances. These derivative instruments are designated as cash flow hedges for accounting purposes, with changes in fair value prior to occurrence of the hedged transactions recorded as other comprehensive loss. As of Dec. 31, 2023, accumulated other comprehensive loss related to interest rate derivatives included immaterial net losses expected to be reclassified into earnings during the next 12 months as the hedged transactions impact earnings. As of Dec. 31, 2023, SPS had no unsettled interest rate derivatives. Wholesale and Commodity Trading — 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. Derivative instruments entered into for trading purposes are presented in the statements of income as electric revenues, net of any sharing with customers. These activities are not intended to mitigate commodity price risk associated with regulated electric operations. Sharing of these margins is determined through state regulatory proceedings as well as the operation of the FERC-approved joint operating agreement. 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. The most significant derivative positions outstanding at December 31, 2023 and 2022 for this purpose relate to FTR instruments administered by SPP. These instruments are intended to offset the impacts of transmission system congestion. Higher congestion costs in recent years have led to an increase in the fair value of FTRs. Settlements of FTRs are shared with electric customers through fuel and purchased energy cost-recovery mechanisms. When SPS enters into derivative instruments that mitigate commodity price risk on behalf of electric customers, the instruments are not typically designated as qualifying hedging transactions. The classification of unrealized losses or gains on these instruments as a regulatory asset or liability, if applicable, is based on approved regulatory recovery mechanisms. Gross notional amounts of FTRs: (Amounts in Millions) (a) Dec. 31, 2023 Dec. 31, 2022 MWh of electricity 8 8 (a) 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 on 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. As of Dec. 31, 2023, two of SPS’ eight most significant counterparties for these activities, comprising $5 million or 19% of this credit exposure, had investment grade credit ratings from S&P Global Ratings, Moody’s Investor Services, or Fitch Ratings. Five of the eight most significant counterparties, comprising $23 million or 81% of this credit exposure, were not rated by these external ratings agencies, but based on SPS’ internal analysis, had credit quality consistent with investment grade. One of these significant counterparties, comprising an immaterial amount or less than 1% of this credit exposure, had credit quality less than investment grade, based on internal analysis. These eight significant counterparties are municipal or cooperative electric entities, RTOs or other utilities. Recurring Derivative Fair Value Measurements Impact of derivative activity: Pre-Tax Fair Value Gains (Losses) Recognized During the Period in: (Millions of Dollars) Regulatory (Assets) and Liabilities Year Ended Dec. 31, 2023 Other derivative instruments Electric commodity $ (88) Total $ (88) Year Ended Dec. 31, 2022 Other derivative instruments Electric commodity $ (3) Total $ (3) Year Ended Dec. 31, 2021 Other derivative instruments Electric commodity $ 28 Total $ 28 Pre-Tax (Gains) Losses Reclassified into Income During the Period from: (Millions of Dollars) Regulatory Year Ended Dec. 31, 2023 Other derivative instruments Electric commodity 78 (a) Total $ 78 Year Ended Dec. 31, 2022 Other derivative instruments Electric commodity 2 (a) Total $ 2 Year Ended Dec. 31, 2021 Other derivative instruments Electric commodity (20) (a) Total $ (20) (a) 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 years ended Dec. 31, 2023, 2022 and 2021. Derivative assets and liabilities measured at fair value on a recurring basis were as follows: Dec. 31, 2023 Dec. 31, 2022 Fair Value Fair Value Total Netting (a) Total Fair Value Fair Value Total Netting (a) Total (Millions of Dollars) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Current derivative assets Other derivative instruments: Electric commodity $ — $ — $ 39 $ 39 $ — $ 39 $ — $ — $ 119 $ 119 $ — $ 119 Total current derivative assets $ — $ — $ 39 $ 39 $ — 39 $ — $ — $ 119 $ 119 $ — 119 PPAs (b) 3 3 Current derivative instruments $ 42 $ 122 Noncurrent derivative assets PPAs (b) $ — $ 3 Noncurrent derivative instruments $ — $ 3 Current derivative liabilities Other derivative instruments: PPAs (b) $ 2 $ 4 Current derivative instruments $ 2 $ 4 Noncurrent derivative liabilities PPAs (b) $ — $ 2 Noncurrent derivative instruments $ — $ 2 (a) SPS nets derivative instruments and related collateral on its balance sheet when supported by a legally enforceable master netting agreement. At Dec. 31, 2023 and 2022, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. Counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements. (b) SPS currently applies the normal purchase exception to qualifying PPAs. Balance relates to specific contracts that were previously recognized at fair value prior to applying the normal purchase exception, and are being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities. Changes in Level 3 commodity derivatives: Year Ended Dec. 31 (Millions of Dollars) 2023 2022 2021 Balance at Jan. 1 $ 119 $ 27 $ 7 Purchases (a) 79 248 10 Settlements (a) (89) (168) (79) Net transactions recorded during the period: Net (losses) gains recognized as regulatory assets and liabilities (a) (70) 12 89 Balance at Dec. 31 $ 39 $ 119 $ 27 (a) Relates primarily to FTR instruments administered by SPP. Fair Value of Long-Term Debt As of Dec. 31, other financial instruments for which the carrying amount did not equal fair value: 2023 2022 (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Long-term debt $ 3,311 $ 2,818 $ 3,211 $ 2,674 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 Dec. 31, 2023 and 2022, and given the observability of the inputs, fair values presented for long-term debt were assigned as Level 2.

Benefit Plans and Other Postret

Benefit Plans and Other Postretirement Benefits	12 Months Ended
	Dec. 31, 2023
Retirement Benefits [Abstract]
Benefit Plans and Other Postretirement Benefits	9. Benefit Plans and Other Postretirement Benefits Pension and Postretirement Health Care Benefits Xcel Energy, which includes SPS, has several noncontributory, qualified, defined benefit pension plans that cover almost all employees. All newly hired or rehired employees participate under the Cash Balance formula, which is based on pay credits using a percentage of annual eligible pay and annual interest credits. The average annual interest crediting rates for these plans was 4.45, 4.69 and 2.35 percent in 2023, 2022, and 2021, respectively. Some employees may participate under legacy formulas such as the traditional final average pay or pension equity. Xcel Energy’s policy is to fully fund into an external trust the actuarially determined pension costs subject to the limitations of applicable employee benefit and tax laws. In addition to the qualified pension plans, Xcel Energy maintains a SERP and a nonqualified pension plan. The SERP is maintained for certain executives who participated in the plan in 2008, when the SERP was closed to new participants. The nonqualified pension plan provides benefits for compensation that is in excess of the limits applicable to the qualified pension plans, with distributions funded by Xcel Energy’s consolidated operating cash flows. Obligations of the SERP and nonqualified plan as of Dec. 31, 2023 and 2022 were $12 million and $11 million, respectively, of which $1 million was attributable to SPS in 2023 and 2022. In 2023 and 2022, Xcel Energy recognized net benefit cost for the SERP and nonqualified plans of $2 million and $17 million, respectively, of which immaterial amounts were attributable to SPS. Xcel Energy’s postretirement health care benefit plan is a continuation of certain welfare benefit programs for current employees. A full time employee’s date of hire or a retiree’s date of retirement determine eligibility for each of the programs. Xcel Energy’s investment-return assumption considers the expected long-term performance for each of the asset classes in its pension and postretirement health care portfolio. Xcel Energy considers the historical returns achieved by its asset portfolios over long time periods, as well as the long-term projected return levels from investment experts. Xcel Energy and SPS continually review pension assumptions. Pension cost determination assumes a forecasted mix of investment types over the long-term. • Investment returns in 2023 were above the assumed level of 6.96%. • Investment returns in 2022 were below the assumed level of 6.39%. • Investment returns in 2021 were above the assumed level of 6.39%. • In 2024, SPS’ expected investment-return assumption is 6.97%. Pension plan and postretirement benefit assets are invested in a portfolio according to Xcel Energy’s return, liquidity and diversification objectives to provide a source of funding for plan obligations and minimize contributions to the plan, within appropriate levels of risk. The principal mechanism for achieving these objectives is the asset allocation given the long-term risk, return, correlation and liquidity characteristics of each particular asset class. There were no significant concentrations of risk in any industry, index, or entity. Market volatility can impact even well-diversified portfolios and significantly affect the return levels achieved by the assets in any year. State agencies also have issued guidelines to the funding of postretirement benefit costs. SPS is required to fund postretirement benefit plans for Texas and New Mexico equal to amounts collected in rates. These assets are invested in a manner consistent with the investment strategy for the pension plan. Xcel Energy’s ongoing investment strategy is based on plan-specific investment recommendations that seek to minimize potential investment and interest rate risk as a plan’s funded status increases over time. The investment recommendations consider many factors and generally result in a greater percentage of long-duration fixed income securities being allocated to specific plans having relatively higher funded status ratios and a greater percentage of growth assets being allocated to plans having relatively lower funded status ratios. Plan Assets For each of the fair value hierarchy levels, SPS’ pension plan assets measured at fair value: Dec. 31, 2023 (a) Dec. 31, 2022 (a) (Millions of Dollars) Level 1 Level 2 Level 3 Measured at NAV Total Level 1 Level 2 Level 3 Measured at NAV Total Cash equivalents $ 38 $ — $ — $ — $ 38 $ 21 $ — $ — $ — $ 21 Commingled funds 72 — — 190 262 144 — — 129 273 Debt securities — 116 1 — 117 — 115 — — 115 Equity securities 5 — — — 5 7 — — — 7 Other — (2) — — (2) — 1 — — 1 Total $ 115 $ 114 $ 1 $ 190 $ 420 $ 172 $ 116 $ — $ 129 $ 417 (a) See Note 8 for further information on fair value measurement inputs and methods. For each of the fair value hierarchy levels, SPS’ proportionate allocation of the total postretirement benefit plan assets that were measured at fair value: Dec. 31, 2023 (a) Dec. 31, 2022 (a) (Millions of Dollars) Level 1 Level 2 Level 3 Measured at NAV Total Level 1 Level 2 Level 3 Measured at NAV Total Cash equivalents $ 3 $ — $ — $ — $ 3 $ 3 $ — $ — $ — $ 3 Insurance contracts — 5 — — 5 — 4 — — 4 Commingled funds 2 — — 7 9 5 — — 6 11 Debt securities — 19 — — 19 — 18 — — 18 Total $ 5 $ 24 $ — $ 7 $ 36 $ 8 $ 22 $ — $ 6 $ 36 (a) See Note 8 for further information on fair value measurement inputs and methods. Immaterial assets were transferred in or out of Level 3 for 2023 and no assets were transferred in or out of Level 3 for 2022. Funded Status — Comparisons of the actuarially computed benefit obligation, changes in plan assets and funded status of the pension and postretirement health care plans for SPS are as follows: Pension Benefits Postretirement Benefits (Millions of Dollars) 2023 2022 2023 2022 Change in Benefit Obligation: Obligation at Jan. 1 $ 414 $ 545 $ 26 $ 34 Service cost 7 10 1 1 Interest cost 22 16 1 1 Actuarial (gain) loss 16 (123) 1 (8) Plan participants’ contributions — — 1 1 Benefit payments (34) (34) (4) (3) Obligation at Dec. 31 $ 425 $ 414 $ 26 $ 26 Change in Fair Value of Plan Assets: Fair value of plan assets at Jan. 1 $ 417 $ 557 $ 36 $ 43 Actual return on plan assets 37 (106) 3 (5) Plan participants’ contributions — — 1 1 Benefit payments (34) (34) (4) (3) Fair value of plan assets at Dec. 31 $ 420 $ 417 $ 36 $ 36 Funded status of plans at Dec. 31 $ (5) $ 3 $ 10 $ 10 Amounts recognized in the Balance Sheet at Dec. 31: Noncurrent assets 1 7 10 10 Noncurrent liabilities (6) (4) — — Net amounts recognized $ (5) $ 3 $ 10 $ 10 Pension Benefits Postretirement Benefits Significant Assumptions Used to Measure Benefit Obligations: 2023 2022 2023 2022 Discount rate for year-end valuation 5.49 % 5.80 % 5.54 % 5.80 % Expected average long-term increase in compensation level 4.25 % 4.25 % N/A N/A Mortality table Pri-2012 Pri-2012 Pri-2012 Pri-2012 Health care costs trend rate — initial: Pre-65 N/A N/A 6.50 % 6.50 % Health care costs trend rate — initial: Post-65 N/A N/A 5.50 % 5.50 % Ultimate trend assumption — initial: Pre-65 N/A N/A 4.50 % 4.50 % Ultimate trend assumption — initial: Post-65 N/A N/A 4.50 % 4.50 % Years until ultimate trend is reached N/A N/A 6 7 Accumulated benefit obligation for the pension plan was $395 million and $386 million as of Dec. 31, 2023 and 2022, respectively. Net Periodic Benefit Cost (Credit) — Net periodic benefit cost (credit), other than the service cost component, is included in other income, net in the statements of income. Components of net periodic benefit cost (credit) and amounts recognized in other comprehensive income and regulatory assets and liabilities: Pension Benefits Postretirement Benefits (Millions of Dollars) 2023 2022 2021 2023 2022 2021 Service cost $ 7 $ 10 $ 11 $ 1 $ 1 $ 1 Interest cost 22 16 15 1 1 1 Expected return on plan assets (32) (31) (30) (1) (2) (2) Amortization of net loss (gain) 2 10 14 — — (1) Settlement charge (a) — 2 — — — — Net periodic pension cost (1) 7 10 1 — (1) Effects of regulation 5 (1) — — — — Net benefit cost recognized for financial reporting $ 4 $ 6 $ 10 $ 1 $ — $ (1) Significant Assumptions Used to Measure Costs: Discount rate 5.80 % 3.08 % 2.71 % 5.80 % 3.09 % 2.65 % Expected average long-term increase in compensation level 4.25 3.75 3.75 — — — Expected average long-term rate of return on assets 6.96 6.39 6.39 5.00 4.10 4.10 (a) A settlement charge is required when the amount of all 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 2022, as a result of lump-sum distributions during each plan year, SPS recorded a total pension settlement charge of $2 million. An immaterial amount was recorded in the income statement in 2022. There were no settlement charges recorded to the qualified pension plans in 2023 or 2021. Pension Benefits Postretirement Benefits (Millions of Dollars) 2023 2022 2023 2022 Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost: Net loss (gain) $ 155 $ 145 $ (20) $ (21) Prior service credit (1) (1) — — Total $ 154 $ 144 $ (20) $ (21) 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 $ 2 $ 2 $ — $ — Noncurrent regulatory assets 152 142 — — Current regulatory liabilities — — (1) (1) Noncurrent regulatory liabilities — — (19) (20) Total $ 154 $ 144 $ (20) $ (21) Measurement date Dec. 31, 2023 Dec. 31, 2022 Dec. 31, 2023 Dec. 31, 2022 Cash Flows — Funding requirements can be impacted by changes to actuarial assumptions, actual asset levels and other calculations prescribed by the requirements of income tax and other pension-related regulations. Required contributions were made in 2021 - 2024 to meet minimum funding requirements. Total voluntary and required pension funding contributions across all four of Xcel Energy’s pension plans were as follows: • $100 million in January 2024, of which $3 million was attributable to SPS. • $50 million in 2023, of which none was attributable to SPS. • $50 million in 2022, of which none was attributable to SPS. • $131 million in 2021, of which $15 million was attributable to SPS. For future years, Xcel Energy and SPS anticipate contributions will be made as necessary. The postretirement health care plans have no funding requirements other than fulfilling benefit payment obligations when claims are presented and approved. Additional cash funding requirements are prescribed by certain state and federal rate regulatory authorities. Xcel Energy’s voluntary postretirement funding contributions, of which the amounts attributable to SPS were immaterial, were as follows: • $11 million expected in 2024. • $11 million during 2023. • $13 million during 2022. • $15 million during 2021. Target asset allocations: Pension Benefits Postretirement Benefits 2023 2022 2023 2022 Long-duration fixed income securities 38 % 38 % — % — % Domestic and international equity securities 31 33 9 16 Alternative investments 20 18 13 12 Short-to-intermediate fixed income securities 9 9 77 71 Cash 2 2 1 1 Total 100 % 100 % 100 % 100 % The asset allocations above reflect target allocations approved in the calendar year to take effect in the subsequent year Plan Amendments — In 2023, Xcel Energy amended the Xcel Energy Pension Plan and Xcel Energy Inc. Nonbargaining Pension Plan (South) to reduce supplemental social security benefits for all active participants on and after Jan. 1, 2024. There were no significant plan amendments made in 2022 which affected the postretirement benefit obligation. In 2021, Xcel Energy amended the Xcel Energy Pension Plan and Xcel Energy Inc. Nonbargaining Pension Plan (South) to reduce supplemental benefits for non-bargaining participants as well as to allow the transfer of a portion of non-qualified pension obligations into the qualified plans. Voluntary Retirement Program Incremental to amounts presented above for postretirement benefits, Xcel Energy, which includes SPS, recognized new postemployment costs and obligations in the fourth quarter of 2023 for employees accepted to a voluntary retirement program. Utilizing employee information and the following inputs, the estimated SPS obligations for the program of $1 million for health plan subsidies and an immaterial amount for other medical benefits, each commencing in 2024, were recognized in the fourth quarter of 2023. These unfunded obligations are presented in other current liabilities and noncurrent pension and employee benefit obligations in the balance sheet as of Dec. 31, 2023. Significant Assumptions to Measure Benefit Obligations: 2023 Discount rate for year-end valuation 5.50 % Mortality table PRI-2012 Health care costs trend rate and ultimate trend assumption 7.00 % Projected Benefit Payments SPS’ projected benefit payments: (Millions of Dollars) Projected Net Projected Postretirement Health Care Benefit Payments (a) 2024 $ 36 $ 2 2025 29 2 2026 30 2 2027 31 2 2028 32 2 2029-2033 157 10 (a) Amount is reported net of expected Medicare Part D subsidies, which are immaterial. Defined Contribution Plans Xcel Energy, which includes SPS, maintains 401(k) and other defined contribution plans that cover most employees. The expense to these plans for SPS was approximately $4 million in 2023, and $3 million in 2022 and 2021, respectively.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	11. Related Party Transactions Xcel Energy Services Inc. provides management, administrative and other services for the subsidiaries of Xcel Energy Inc., including SPS. The services are provided and billed to each subsidiary in accordance with service agreements executed by each subsidiary. SPS uses services provided by Xcel Energy Services Inc. whenever possible. Costs are charged directly to the subsidiary and are allocated if they cannot be directly assigned. Xcel Energy, Inc., NSP-Minnesota, NSP-Wisconsin, PSCo and SPS have established a utility money pool arrangement. See Note 5 for further information. Significant affiliate transactions among the companies and related parties for the years ended Dec. 31: (Millions of Dollars) 2023 2022 2021 Operating expenses: Other operating expenses — paid to Xcel Energy Services Inc. $ 245 $ 238 $ 209 Interest expense 4 1 — Accounts receivable and payable with affiliates at Dec. 31 were: 2023 2022 (Millions of Dollars) Accounts Receivable Accounts Payable Accounts Receivable Accounts Payable NSP-Minnesota $ 4 $ — $ 3 $ — PSCo 11 — 11 — Other subsidiaries of Xcel Energy Inc. 11 7 1 23 $ 26 $ 7 $ 15 $ 23

Compensation Related Costs, Pos

Compensation Related Costs, Postemployment Benefits	12 Months Ended
	Dec. 31, 2023
Postemployment Benefits [Abstract]
Postemployment Benefits Disclosure	In 2023, Xcel Energy implemented workforce actions to align resources and investments with evolving business and customer needs, and streamline the organization for long-term success. In September 2023, Xcel Energy announced a voluntary retirement program to a group of eligible non-bargaining employees, with an enhanced retirement package including certain health care and cash benefits for accepted employees. Approximately 400 employees retired under this program in December 2023. In November 2023, Xcel Energy, Inc. also reduced its non-bargaining workforce by approximately 150 employees through an involuntary severance program. In the fourth quarter of 2023, Xcel Energy recorded total expense of $72 million related to these workforce actions, of which $9 million was attributable to SPS. Expenses relate to the estimated cost of future health plan subsidies and other medical benefits for the voluntary retirement program, as well as severance and other employee payouts and legal and other professional fees.

Schedule II, Valuation and Qual

Schedule II, Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2023
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II, Valuation and Qualifying Accounts	Southwestern Public Service Co. Valuation and Qualifying Accounts Years Ended Dec. 31 Allowance for bad debts (Millions of Dollars) 2023 2022 2021 Balance at Jan. 1 $ 13 $ 12 $ 8 Additions charged to costs and expenses 11 9 6 Additions charged to other accounts (a) 1 1 3 Deductions from reserves (b) (10) (9) (5) Balance at Dec. 31 $ 15 $ 13 $ 12 (a) Recovery of amounts previously written-off. (b) Deductions related primarily to bad debt write-offs.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Business and System of Accounts	General — SPS is engaged in the regulated generation, purchase, transmission, distribution and sale of electricity. SPS’ financial statements are presented in accordance with GAAP. All of SPS’ underlying accounting records also conform to the FERC uniform system of accounts or to systems required by various state regulatory commissions. Certain amounts in the financial statements or notes have been reclassified for comparative purposes; however, such reclassifications did not affect net income, total assets, liabilities, equity or cash flows.
Subsequent Events	SPS has evaluated events occurring after Dec. 31, 2023 up to the date of issuance of these financial statements. These statements contain all necessary adjustments and disclosures resulting from that evaluation.
Use of Estimates	Use of Estimates — SPS uses estimates based on the best information available to record transactions and balances resulting from business operations. Estimates are used for items such as plant depreciable lives or potential disallowances, AROs, certain regulatory assets and liabilities, tax provisions, uncollectible amounts, environmental costs, unbilled revenues, jurisdictional fuel and energy cost allocations and actuarially determined benefit costs. Recorded estimates are revised when better information becomes available or actual amounts can be determined. Revisions can affect operating results.
Regulatory Accounting	Regulatory Accounting — SPS accounts for income and expense items in accordance with accounting guidance for regulated operations. Under this guidance: • Certain costs, which would otherwise be charged to expense or other comprehensive income, are deferred as regulatory assets based on the expected ability to recover the costs in future rates. • Certain credits, which would otherwise be reflected as income or other comprehensive income, are deferred as regulatory liabilities based on the expectation the amounts will be returned to customers in future rates or because the amounts were collected in rates prior to the costs being incurred. Estimates and assumptions for recovery of deferred costs and refund of deferred credits are based on specific ratemaking decisions, precedent or other available information. Regulatory assets and liabilities are amortized consistent with the treatment in the rate setting process. If changes in the regulatory environment occur, SPS may no longer be eligible to apply this accounting treatment and may be required to eliminate regulatory assets and liabilities. Such changes could have a material effect on SPS’ results of operations, financial condition and cash flows. See Note 4 for further information.
Income Taxes	Income Taxes — SPS accounts for income taxes using the asset and liability method, which requires recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Income taxes are deferred for all temporary differences between pretax financial and taxable income and between the book and tax bases of assets and liabilities utilizing rates that are scheduled to be in effect when the temporary differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the period that includes the enactment date. Utility rate regulation has resulted in the recognition of regulatory assets and liabilities related to income taxes. The effects of SPS’ tax rate changes are generally subject to a normalization method of accounting. Therefore, the revaluation of most of its net deferred taxes upon a tax rate reduction results in the establishment of a net regulatory liability, refundable to utility customers over the remaining life of the related assets. SPS anticipates that a tax rate increase would predominantly result in the establishment of a regulatory asset, subject to an evaluation of whether future recovery is expected. Tax credits are recorded when earned unless there is a requirement to defer the benefit and amortize over the book depreciable lives of related property. The requirement to defer and amortize these credits specifically applies to certain federal ITCs, as determined by tax regulations and SPS tax elections. For tax credits otherwise eligible to be recognized when earned, SPS considers the impact of rate regulation to determine if these credits and related adjustments should be deferred as regulatory assets or liabilities. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that some portion or all of the deferred tax asset will not be realized. This evaluation includes consideration of whether tax credits are expected to be sold at a discount and impact the realization of amounts presented as deferred tax assets. Transferable tax credits are accounted for under ASC 740 Income Taxes , and valuation allowances and any adjustments for discounts incurred on sales transactions are recorded to deferred tax expense. SPS measures and discloses uncertain tax positions that it has taken or expects to take in its income tax returns. A tax position is recognized in the financial statements when it is more likely than not that the position will be sustained upon examination based on the technical merits of the position. Recognition of changes in uncertain tax positions are reflected as a component of income tax expense. Interest and penalties related to income taxes are reported within Other income, net or interest charges in the statements of income. Xcel Energy Inc. and its subsidiaries, including SPS file consolidated federal income tax returns as well as consolidated or separate state income tax returns. Federal income taxes paid by Xcel Energy Inc. are allocated to its subsidiaries based on separate company computations. A similar allocation is made for state income taxes paid by Xcel Energy Inc. in connection with consolidated state filings. Xcel Energy Inc. also allocates its own income tax benefits to its direct subsidiaries. See Note 7 for further information.
Property, Plant and Equipment and Depreciation	Property, Plant and Equipment and Depreciation in Regulated Operations — Property, plant and equipment is stated at original cost. The cost of plant includes direct labor and materials, contracted work, overhead costs and AFUDC. The cost of plant retired is charged to accumulated depreciation and amortization. Amounts recovered in rates for future removal costs are recorded as regulatory liabilities. Significant additions or improvements extending asset lives are capitalized, while repairs and maintenance costs and replacement of items determined to be less than a unit of property are charged to expense as incurred. Property, plant and equipment is tested for impairment when it is determined that the carrying value of the assets may not be recoverable. A loss is recognized in the current period if it becomes probable that part of a cost of a plant under construction or recently completed plant will be disallowed for recovery from customers and a reasonable estimate of the disallowance can be made. For investments in property, plant and equipment that are abandoned and not expected to go into service, incurred costs and related deferred tax amounts are compared to the discounted estimated future rate recovery, and a loss is recognized, if necessary. Depreciation expense is recorded using the straight-line method over the plant’s commission approved useful life. Actuarial life studies are performed and submitted to the state and federal commissions for review. Upon acceptance by the various commissions, the resulting lives and net salvage rates are used to calculate depreciation. Plant removal costs are typically recognized at the amounts recovered in rates as authorized by the applicable regulator. Accumulated removal costs are reflected in the balance sheet as a regulatory liability. Depreciation expense, expressed as a percentage of average depreciable property, was 3.4% in 2023, 3.4% in 2022 and 3.3% in 2021. See Note 3 for further information.
Asset Retirement Obligations	AROs — SPS records AROs as a liability in the period incurred (if fair value can be reasonably estimated), with the offsetting/associated costs capitalized as a long-lived asset. The liability is generally increased over time by applying the effective interest method of accretion and the capitalized costs are typically depreciated over the useful life of the long-lived asset. Changes resulting from revisions to timing or amounts of expected asset retirement cash flows are recognized as an increase or a decrease in the ARO. See Note 10 for further information.
Benefit Plans and Other Postretirement Benefits	Benefit Plans and Other Postretirement Benefits — SPS maintains pension and postretirement benefit plans for eligible employees. Recognizing the cost of providing benefits and measuring the projected benefit obligation of these plans requires management to make various assumptions and estimates. Certain unrecognized actuarial gains and losses and unrecognized prior service costs or credits are deferred as regulatory assets and liabilities, rather than recorded as other comprehensive income, based on regulatory recovery mechanisms. See Note 9 for further information.
Environmental Costs	Environmental Costs — Environmental costs are recorded when it is probable SPS is liable for remediation costs and the amount can be reasonably estimated. Costs are deferred as a regulatory asset if it is probable the costs will be recovered from customers in future rates. Otherwise, the costs are expensed. For certain environmental costs related to facilities currently in use, such as for emission-control equipment, the cost is capitalized and depreciated over the life of the plant. Estimated remediation costs are regularly adjusted as estimates are revised and remediation is performed. If other participating potentially responsible parties exist and acknowledge their potential involvement with a site, costs are estimated and recorded only for SPS’ expected share of the cost.
Revenue From Contracts With Customers	Revenue from Contracts with Customers — Performance obligations related to the sale of energy are satisfied as energy is delivered to customers. SPS recognizes revenue that corresponds to the price of the energy delivered to the customer. The measurement of energy sales to customers is generally based on the reading of their meters, which occurs systematically throughout the month. At the end of each month, amounts of energy delivered to customers since the date of the last meter reading are estimated and the corresponding unbilled revenue is recognized. A separate financing component of collections from customers is not recognized as contract terms are short-term in nature. Revenues are net of any excise or sales taxes or fees. SPS participates in SPP. SPS recognizes physical sales to customers (native load and wholesale) on a gross basis in electric revenues and cost of sales. Revenues and charges for short-term physical wholesale sales of excess energy transacted through RTOs are also recorded on a gross basis. Other revenues and charges settled/facilitated through an RTO are recorded on a net basis in cost of sales. See Note 6 for further information.
Cash and Cash Equivalents	Cash and Cash Equivalents — SPS considers investments in instruments with a remaining maturity of 3 months or less at the time of purchase to be cash equivalents.
Accounts Receivable and Allowance for Bad Debts	Accounts Receivable and Allowance for Bad Debts — Accounts receivable are stated at the actual billed amount net of an allowance for bad debts. SPS establishes an allowance for uncollectible receivables based on a policy that reflects its expected exposure to the credit risk of customers.
Inventory	Inventory — Inventory is recorded at the lower of average cost or net realizable value and consisted of the following: (Millions of Dollars) Dec. 31, 2023 Dec. 31, 2022 Inventories Materials and supplies $ 56 $ 42 Fuel 13 19 Total inventories $ 69 $ 61
Fair Value Measurements	Fair Value Measurements — SPS presents cash equivalents, interest rate derivatives and commodity derivatives at estimated fair values in its financial statements. For interest rate derivatives, quoted prices based primarily on observable market interest rate curves are used to estimate fair value. For commodity derivatives, the most observable inputs available are generally used to determine the fair value of each contract. In the absence of a quoted price, quoted prices for similar contracts or internally prepared valuation models may be used to determine fair value. For the pension and postretirement plan assets and nuclear decommissioning fund, published trading data and pricing models, generally using the most observable inputs available, are utilized to determine fair value for each security. See Notes 8 and 9 for further information.
Derivative Instruments	Derivative Instruments — SPS uses derivative instruments in connection with its commodity trading activities, and to manage risk associated with changes in interest rates and utility commodity prices, including forward contracts, futures, swaps and options. Derivatives not qualifying for the normal purchases and normal sales exception are recorded on the balance sheets at fair value as derivative instruments. Classification of changes in fair value for those derivative instruments is dependent on the designation of a qualifying hedging relationship. Changes in fair value of derivative instruments not designated in a qualifying hedging relationship are reflected in current earnings or as a regulatory asset or liability. Classification as a regulatory asset or liability is based on commission approved regulatory recovery mechanisms. Gains or losses on commodity trading transactions are recorded as a component of electric operating revenues. Normal Purchases and Normal Sales — SPS enters into contracts for purchases and sales of commodities for use in its operations. At inception, contracts are evaluated to determine whether they contain a derivative, and if so, whether they may be exempted from derivative accounting if designated as normal purchases or normal sales. See Note 8 for further information.
AFUDC	AFUDC — AFUDC represents the cost of capital used to finance utility construction activity and is computed by applying a composite financing rate to qualified CWIP. The amount of AFUDC capitalized as a utility construction cost is credited to other nonoperating income (for equity capital) and interest charges (for debt capital). AFUDC amounts capitalized are included in SPS’ rate base.
Alternative Revenue Programs	Alternative Revenue — Certain rate rider mechanisms (including DSM programs) qualify as alternative revenue programs. These mechanisms arise from instances in which the regulator authorizes a future surcharge in response to past activities or completed events. When certain criteria are met, including expected collection within 24 months, revenue is recognized equal to the revenue requirement, which may include incentives and return on rate base items. Billing amounts are revised periodically for differences between total amount collected and revenue earned, which may increase or decrease the level of revenue collected from customers. Alternative revenues arising from these programs are presented on a gross basis and disclosed separately from revenue from contracts with customers. See Note 6 for further information. Conservation Programs — SPS has implemented programs in its jurisdictions to assist customers in conserving energy and reducing peak demand on the electric system. These programs include commercial motor, air conditioner and lighting upgrades, as well as residential rebates for participation in air conditioner interruption and home weatherization. The costs incurred for some DSM programs are deferred as permitted by the applicable regulatory jurisdiction. For those programs, costs are deferred if it is probable future revenue will be provided to permit recovery of the incurred cost. Revenues recognized for incentive programs designed for recovery of lost margins and/or conservation performance incentives are limited to amounts expected to be collected within 24 months from the annual period in which they are earned. SPS recovers approved conservation program costs in base rate revenue or through a rider.
Emission Allowances	Emissions Allowances — Emissions allowances are recorded at cost, including broker commission fees. The inventory accounting model is utilized for all emission allowances and sales of these allowances are included in electric revenues.
Renewable Energy Credits	RECs — Cost of RECs that are utilized for compliance is recorded as electric fuel and purchased power expense. SPS reduces recoverable fuel and purchased power costs for the cost of RECs received. An inventory accounting model is used to account for RECs, however these assets are classified as regulatory assets if amounts are recoverable in future rates.
Segment Reporting, Policy [Policy Text Block]	Segment Information

Summary of Significant Accoun_3

Summary of Significant Accounting Policies Inventory (Tables)	12 Months Ended
	Dec. 31, 2023
Balance Sheet Related Disclosure - Inventory [Abstract]
Schedule of Utility Inventory [Table Text Block]	Inventory — Inventory is recorded at the lower of average cost or net realizable value and consisted of the following: (Millions of Dollars) Dec. 31, 2023 Dec. 31, 2022 Inventories Materials and supplies $ 56 $ 42 Fuel 13 19 Total inventories $ 69 $ 61

Property Plant and Equipment _2

Property Plant and Equipment Property Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Public Utility Property, Plant, and Equipment	Major classes of property, plant and equipment (Millions of Dollars) Dec. 31, 2023 Dec. 31, 2022 Property, plant and equipment, net Electric plant $ 10,752 $ 10,182 Plant to be retired (a) 248 266 CWIP 226 167 Total property, plant and equipment 11,226 10,615 Less accumulated depreciation (2,690) (2,486) Property, plant and equipment, net $ 8,536 $ 8,129 (a) Amounts include Tolk Unit 1 and 2 and coal generation assets at Harrington pending facility gas conversion. Amounts are reported net of accumulated depreciation.

Regulatory Assets and Liabili_2

Regulatory Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2023
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	Components of regulatory assets: (Millions of Dollars) See Note(s) Remaining Amortization Period Dec. 31, 2023 Dec. 31, 2022 (a) Regulatory Assets Current Noncurrent Current Noncurrent Pension and retiree medical obligations 9 Various $ 2 $ 147 $ 2 $ 146 Net AROs (b) 1, 10 Various — 59 — 48 Excess deferred taxes — TCJA 7 Various 1 47 1 48 Recoverable deferred taxes on AFUDC Plant lives — 44 — 40 Losses on reacquired debt Term of related debt 1 18 1 19 Deferred electric energy/fuel costs N/A — — 136 34 Other Various 26 34 77 24 Total regulatory assets $ 30 $ 349 $ 217 $ 359 (a) Prior period amounts have been restated to conform with current year presentation. (b) Includes amounts recorded for future recovery of AROs.
Regulatory Liabilities	Components of regulatory liabilities: (Millions of Dollars) See Note(s) Remaining Amortization Period Dec. 31, 2023 Dec. 31, 2022 (a) Regulatory Liabilities Current Noncurrent Current Noncurrent Deferred income tax adjustments and TCJA refunds (b) 7 Various $ — $ 458 $ — $ 469 Plant removal costs 1, 10 Various — 223 — 198 LP&L departure payment Up to 10 years 33 33 — — Effects of regulation on employee benefit costs Various — 19 — 20 Formula rates One two 13 10 10 8 Renewable resources and environmental initiatives Various — 8 — 14 Contract valuation adjustments (c) 1, 8 Less than one 41 — 119 1 Deferred electric energy costs Less than one 15 — — — Other Various 14 10 19 5 Total regulatory liabilities $ 116 $ 761 $ 148 $ 715 (a) Prior period amounts have been reclassified to conform with current year presentation. (b) Includes the revaluation of recoverable/regulated plant accumulated deferred income taxes and revaluation impact of non-plant accumulated deferred income taxes due to the TCJA. (c) Includes the fair value of FTR instruments utilized/intended to offset the impacts of transmission system congestion.

Borrowings and Other Financin_2

Borrowings and Other Financing Instruments (Tables)	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Money Pool [Table Text Block]	Money pool borrowings: (Millions of Dollars, Except Interest Rates) Three Months Ended Dec. 31, 2023 Year Ended Dec. 31 2023 2022 2021 Borrowing limit $ 100 $ 100 $ 100 $ 100 Amount outstanding at period end 27 27 — 91 Average amount outstanding 14 46 35 51 Maximum amount outstanding 44 100 100 100 Weighted average interest rate, computed on a daily basis 5.34 % 5.04 % 0.44 % 0.05 % Weighted average interest rate at end of period 5.34 5.34 N/A 0.05
Short-Term Borrowings	Commercial paper outstanding: (Millions of Dollars, Except Interest Rates) Three Months Ended Dec. 31, 2023 Year Ended Dec. 31 2023 2022 2021 Borrowing limit $ 500 $ 500 $ 500 $ 500 Amount outstanding at period end 75 75 34 137 Average amount outstanding 18 50 100 63 Maximum amount outstanding 95 119 324 342 Weighted average interest rate, computed on a daily basis 5.54 % 5.12 % 0.79 % 0.21 % Weighted average interest rate at end of period 5.56 5.56 4.55 0.26
Schedule Of Debt To Total Capitalization Ratio [Table Text Block]	Features of SPS’ credit facility: Debt-to-Total Capitalization Ratio (a) Amount Facility May Be Increased (millions of dollars) Additional Periods for Which a One-Year Extension May Be Requested (b) 2023 2022 46.1% 45.7% $50 2 (a) The credit facility has a financial covenant requiring that the debt-to-total capitalization ratio be less than or equal to 65%. (b)	[1],[2]
Credit Facilities	SPS had the following committed credit facility available as of Dec. 31, 2023 (in millions) of dollars: Credit Facility (a) Drawn (b) Available $ 500 $ 75 $ 425 (a) This credit facility matures in September 2027. (b) Includes letters of credit and outstanding commercial paper.	[3],[4]
Schedule of Long-term Debt Instruments [Table Text Block]	Long-term debt obligations for SPS as of Dec. 31 (in millions of dollars): Financing Instrument Interest Rate Maturity Date 2023 2022 First mortgage bonds 3.30 % June 15, 2024 $ 150 $ 150 First mortgage bonds 3.30 June 15, 2024 200 200 Unsecured senior notes 6.00 Oct. 1, 2033 100 100 Unsecured senior notes 6.00 Oct. 1, 2036 250 250 First mortgage bonds 4.50 Aug. 15, 2041 200 200 First mortgage bonds 4.50 Aug. 15, 2041 100 100 First mortgage bonds 4.50 Aug. 15, 2041 100 100 First mortgage bonds 3.40 Aug. 15, 2046 300 300 First mortgage bonds 3.70 Aug. 15, 2047 450 450 First mortgage bonds 4.40 Nov. 15, 2048 300 300 First mortgage bonds 3.75 June 15, 2049 300 300 First mortgage bonds 3.15 May 1, 2050 350 350 First mortgage bonds 3.15 May 1, 2050 250 250 First mortgage bonds (a) 5.15 June 1, 2052 200 200 First mortgage bonds (b) 6.00 Sept. 15, 2053 100 — Unamortized discount (10) (10) Unamortized debt issuance cost (29) (29) Current maturities (350) — Total long-term debt $ 2,961 $ 3,211 (a) 2022 financing. (b) 2023 financing.	[5]
Schedule of Maturities of Long-term Debt [Table Text Block]	Maturities of long-term debt: (Millions of Dollars) 2024 $ 350 2025 — 2026 — 2027 — 2028 —
Schedule of Stock by Class [Table Text Block]	SPS has the following preferred stock: Preferred Stock Authorized (Shares) Par Value of Preferred Stock Preferred Stock Outstanding (Shares) 2023 and 2022 10,000,000 1.00 —
Dividend Payment Restrictions [Text Block]	Requirements and actuals as of Dec. 31, 2023: Equity to Total Capitalization Ratio Equity to Total Capitalization Ratio Actual (a) Low High 2023 45.0 % 55.0 % 54.6 % (a) Excludes short-term debt. Unrestricted Retained Earnings Total Capitalization Limit on Total Capitalization (a) $ 617 million $ 7,298 million N/A (a)
[1] All extension requests are subject to majority bank group approval. The credit facility has a financial covenant requiring that the debt-to-total capitalization ratio be less than or equal to 65%. Includes letters of credit and outstanding commercial paper. This credit facility matures in September 2027.

Revenues (Tables)

Revenues (Tables)	12 Months Ended
	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	SPS’ operating revenues consisted of the following: Year Ended Dec. 31 (Millions of Dollars) 2023 2022 2021 Major revenue types Revenue from contracts with customers: Residential $ 442 $ 445 $ 375 C&I (a) 1,094 1,102 842 Other 58 51 38 Total retail 1,594 1,598 1,255 Wholesale 223 407 873 Transmission 296 296 287 Other — 10 6 Total revenue from contracts with customers 2,113 2,311 2,421 Alternative revenue and other 39 115 44 Total revenues $ 2,152 $ 2,426 $ 2,465

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Summary of Statute of Limitations Applicable to Open Tax Years	Tax Year(s) Expiration 2014 - 2016 March 2025 2020 September 2024
Reconciliation of Unrecognized Tax Benefits	Unrecognized tax benefits — permanent vs temporary: (Millions of Dollars) Dec. 31, 2023 Dec. 31, 2022 Unrecognized tax benefit — Permanent tax positions $ 5 $ 5 Unrecognized tax benefit — Temporary tax positions — 4 Total unrecognized tax benefit $ 5 $ 9 Changes in unrecognized tax benefits: (Millions of Dollars) 2023 2022 2021 Balance at Jan. 1 $ 9 $ 8 $ 7 Additions based on tax positions related to the current year 1 1 1 Reductions for tax positions of prior years (5) — — Balance at Dec. 31 $ 5 $ 9 $ 8
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) Dec. 31, 2023 Dec. 31, 2022 NOL and tax credit carryforwards $ (4) $ (8)
Interest Payable related to Unrecognized Tax Benefits	Interest payable related to unrecognized tax benefits: (Millions of Dollars) 2023 2022 2021 Payable for interest related to unrecognized tax benefits at Jan. 1 $ — $ (1) $ (1) Interest expense related to unrecognized tax benefits — 1 — Payable for interest related to unrecognized tax benefits at Dec. 31 $ — $ — $ (1)
NOL and Tax Credit Carryforwards	NOL amounts represent the tax loss that is carried forward and tax credits represent the deferred tax asset. NOL and tax credit carryforwards as of Dec. 31 were as follows: (Millions of Dollars) 2023 2022 Federal NOL carryforward $ — $ 8 Federal tax credit carryforwards 406 294 Valuation allowances for federal credit carryforwards (2) — State NOL carryforwards 3 4
Schedule of Effective Income Tax Rate Reconciliation	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. Effective income tax rate for years ended Dec. 31: 2023 2022 2021 Federal statutory rate 21.0 % 21.0 % 21.0 % State income tax on pretax income, net of federal tax effect 2.4 2.3 2.5 Increases (decreases) in tax from: Wind PTCs (a) (33.5) (35.9) (39.7) Plant regulatory differences (b) (3.3) (3.8) (4.8) Amortization of deficient/(excess) nonplant deferred taxes 0.3 (0.9) (1.1) Other, net (0.2) (0.6) (0.7) Effective income tax rate (13.3) % (17.9) % (22.8) % (a) Wind PTCs net of estimated transfer discounts. Gross wind PTCs are credited to customers (reduction to revenue) and do not materially impact net income. (b) Plant regulatory differences primarily relate to the credit of excess deferred taxes to customers through the average rate assumption method. Income tax benefits associated with the credit are offset by corresponding revenue reductions.
Schedule of Components of Income Tax Expense (Benefit)	Components of income tax expense for years ended Dec. 31: (Millions of Dollars) 2023 2022 2021 Current federal tax expense (benefit) $ 76 $ (65) $ (11) Current state tax expense (benefit) 12 (5) (1) Deferred federal tax (benefit) expense (132) 3 (57) Deferred state tax (benefit) expense (1) 13 9 Deferred change in unrecognized tax expense — 1 1 Total income tax benefit $ (45) $ (53) $ (59) Components of deferred income tax expense as of Dec. 31: (Millions of Dollars) 2023 2022 2021 Deferred tax (benefit) expense excluding items below $ (117) $ 37 $ (23) Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities (16) (20) (24) Deferred tax (benefit) expense $ (133) $ 17 $ (47)
Schedule of Deferred Tax Assets and Liabilities	Components of the net deferred tax liability as of Dec. 31: (Millions of Dollars) 2023 2022 (a) Deferred tax liabilities: Differences between book and tax bases of property $ 1,072 $ 1,015 Operating lease assets 90 97 Regulatory assets 51 61 Pension expense 32 33 Total deferred tax liabilities $ 1,245 $ 1,206 Deferred tax assets: Tax credit carryforward $ 406 $ 294 Regulatory liabilities 95 98 Operating lease liabilities 90 97 Other employee benefits 6 6 Deferred fuel costs 5 (35) NOL carryforward — 2 Tax credit valuation allowances (2) — Other 23 5 Total deferred tax assets 623 467 Net deferred tax liability $ 622 $ 739 (a) Prior periods have been reclassified to conform to current year presentation.
State Summary of Statute of Limitations Applicable to Open Tax Years	SPS is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of Dec. 31, 2023, SPS’ earliest open tax years that are subject to examination by state taxing authorities under applicable statutes of limitations are as follows: State Tax Year(s) Expiration Texas 2016, 2018 May 2024 Texas 2017 July 2025 Texas 2019 August 2024

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Gross Notional Amounts of Commodity FTRs	(Amounts in Millions) (a) Dec. 31, 2023 Dec. 31, 2022 MWh of electricity 8 8 (a) Not reflective of net positions in the underlying commodities.
Derivative Assets and Liabilities Measured at Fair Value on a Recurring Basis by Hierarchy Level	Derivative assets and liabilities measured at fair value on a recurring basis were as follows: Dec. 31, 2023 Dec. 31, 2022 Fair Value Fair Value Total Netting (a) Total Fair Value Fair Value Total Netting (a) Total (Millions of Dollars) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Current derivative assets Other derivative instruments: Electric commodity $ — $ — $ 39 $ 39 $ — $ 39 $ — $ — $ 119 $ 119 $ — $ 119 Total current derivative assets $ — $ — $ 39 $ 39 $ — 39 $ — $ — $ 119 $ 119 $ — 119 PPAs (b) 3 3 Current derivative instruments $ 42 $ 122 Noncurrent derivative assets PPAs (b) $ — $ 3 Noncurrent derivative instruments $ — $ 3 Current derivative liabilities Other derivative instruments: PPAs (b) $ 2 $ 4 Current derivative instruments $ 2 $ 4 Noncurrent derivative liabilities PPAs (b) $ — $ 2 Noncurrent derivative instruments $ — $ 2 (a) SPS nets derivative instruments and related collateral on its balance sheet when supported by a legally enforceable master netting agreement. At Dec. 31, 2023 and 2022, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. Counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements. (b) SPS currently applies the normal purchase exception to qualifying PPAs. Balance relates to specific contracts that were previously recognized at fair value prior to applying the normal purchase exception, and are being 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: Year Ended Dec. 31 (Millions of Dollars) 2023 2022 2021 Balance at Jan. 1 $ 119 $ 27 $ 7 Purchases (a) 79 248 10 Settlements (a) (89) (168) (79) Net transactions recorded during the period: Net (losses) gains recognized as regulatory assets and liabilities (a) (70) 12 89 Balance at Dec. 31 $ 39 $ 119 $ 27 (a) Relates primarily to FTR instruments administered by SPP.
Carrying Amount and Fair Value of Long-term Debt	2023 2022 (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Long-term debt $ 3,311 $ 2,818 $ 3,211 $ 2,674
Derivative Instruments, Gain (Loss)	Impact of derivative activity: Pre-Tax Fair Value Gains (Losses) Recognized During the Period in: (Millions of Dollars) Regulatory (Assets) and Liabilities Year Ended Dec. 31, 2023 Other derivative instruments Electric commodity $ (88) Total $ (88) Year Ended Dec. 31, 2022 Other derivative instruments Electric commodity $ (3) Total $ (3) Year Ended Dec. 31, 2021 Other derivative instruments Electric commodity $ 28 Total $ 28 Pre-Tax (Gains) Losses Reclassified into Income During the Period from: (Millions of Dollars) Regulatory Year Ended Dec. 31, 2023 Other derivative instruments Electric commodity 78 (a) Total $ 78 Year Ended Dec. 31, 2022 Other derivative instruments Electric commodity 2 (a) Total $ 2 Year Ended Dec. 31, 2021 Other derivative instruments Electric commodity (20) (a) Total $ (20) (a) 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.

Benefit Plans and Other Postr_2

Benefit Plans and Other Postretirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2023
Benefit Plans and Other Postretirement Benefits [Abstract]
Target Asset Allocations and Plan Assets Measured at Fair Value	For each of the fair value hierarchy levels, SPS’ pension plan assets measured at fair value: Dec. 31, 2023 (a) Dec. 31, 2022 (a) (Millions of Dollars) Level 1 Level 2 Level 3 Measured at NAV Total Level 1 Level 2 Level 3 Measured at NAV Total Cash equivalents $ 38 $ — $ — $ — $ 38 $ 21 $ — $ — $ — $ 21 Commingled funds 72 — — 190 262 144 — — 129 273 Debt securities — 116 1 — 117 — 115 — — 115 Equity securities 5 — — — 5 7 — — — 7 Other — (2) — — (2) — 1 — — 1 Total $ 115 $ 114 $ 1 $ 190 $ 420 $ 172 $ 116 $ — $ 129 $ 417 (a) See Note 8 for further information on fair value measurement inputs and methods. For each of the fair value hierarchy levels, SPS’ proportionate allocation of the total postretirement benefit plan assets that were measured at fair value: Dec. 31, 2023 (a) Dec. 31, 2022 (a) (Millions of Dollars) Level 1 Level 2 Level 3 Measured at NAV Total Level 1 Level 2 Level 3 Measured at NAV Total Cash equivalents $ 3 $ — $ — $ — $ 3 $ 3 $ — $ — $ — $ 3 Insurance contracts — 5 — — 5 — 4 — — 4 Commingled funds 2 — — 7 9 5 — — 6 11 Debt securities — 19 — — 19 — 18 — — 18 Total $ 5 $ 24 $ — $ 7 $ 36 $ 8 $ 22 $ — $ 6 $ 36 (a) See Note 8 for further information on fair value measurement inputs and methods. Target asset allocations: Pension Benefits Postretirement Benefits 2023 2022 2023 2022 Long-duration fixed income securities 38 % 38 % — % — % Domestic and international equity securities 31 33 9 16 Alternative investments 20 18 13 12 Short-to-intermediate fixed income securities 9 9 77 71 Cash 2 2 1 1 Total 100 % 100 % 100 % 100 %
Funded Status of Plans	Funded Status — Comparisons of the actuarially computed benefit obligation, changes in plan assets and funded status of the pension and postretirement health care plans for SPS are as follows: Pension Benefits Postretirement Benefits (Millions of Dollars) 2023 2022 2023 2022 Change in Benefit Obligation: Obligation at Jan. 1 $ 414 $ 545 $ 26 $ 34 Service cost 7 10 1 1 Interest cost 22 16 1 1 Actuarial (gain) loss 16 (123) 1 (8) Plan participants’ contributions — — 1 1 Benefit payments (34) (34) (4) (3) Obligation at Dec. 31 $ 425 $ 414 $ 26 $ 26 Change in Fair Value of Plan Assets: Fair value of plan assets at Jan. 1 $ 417 $ 557 $ 36 $ 43 Actual return on plan assets 37 (106) 3 (5) Plan participants’ contributions — — 1 1 Benefit payments (34) (34) (4) (3) Fair value of plan assets at Dec. 31 $ 420 $ 417 $ 36 $ 36 Funded status of plans at Dec. 31 $ (5) $ 3 $ 10 $ 10 Amounts recognized in the Balance Sheet at Dec. 31: Noncurrent assets 1 7 10 10 Noncurrent liabilities (6) (4) — — Net amounts recognized $ (5) $ 3 $ 10 $ 10 Pension Benefits Postretirement Benefits Significant Assumptions Used to Measure Benefit Obligations: 2023 2022 2023 2022 Discount rate for year-end valuation 5.49 % 5.80 % 5.54 % 5.80 % Expected average long-term increase in compensation level 4.25 % 4.25 % N/A N/A Mortality table Pri-2012 Pri-2012 Pri-2012 Pri-2012 Health care costs trend rate — initial: Pre-65 N/A N/A 6.50 % 6.50 % Health care costs trend rate — initial: Post-65 N/A N/A 5.50 % 5.50 % Ultimate trend assumption — initial: Pre-65 N/A N/A 4.50 % 4.50 % Ultimate trend assumption — initial: Post-65 N/A N/A 4.50 % 4.50 % Years until ultimate trend is reached N/A N/A 6 7 Accumulated benefit obligation for the pension plan was $395 million and $386 million as of Dec. 31, 2023 and 2022, respectively.
Components of Net Periodic Benefit Costs	Net Periodic Benefit Cost (Credit) — Net periodic benefit cost (credit), other than the service cost component, is included in other income, net in the statements of income. Components of net periodic benefit cost (credit) and amounts recognized in other comprehensive income and regulatory assets and liabilities: Pension Benefits Postretirement Benefits (Millions of Dollars) 2023 2022 2021 2023 2022 2021 Service cost $ 7 $ 10 $ 11 $ 1 $ 1 $ 1 Interest cost 22 16 15 1 1 1 Expected return on plan assets (32) (31) (30) (1) (2) (2) Amortization of net loss (gain) 2 10 14 — — (1) Settlement charge (a) — 2 — — — — Net periodic pension cost (1) 7 10 1 — (1) Effects of regulation 5 (1) — — — — Net benefit cost recognized for financial reporting $ 4 $ 6 $ 10 $ 1 $ — $ (1) Significant Assumptions Used to Measure Costs: Discount rate 5.80 % 3.08 % 2.71 % 5.80 % 3.09 % 2.65 % Expected average long-term increase in compensation level 4.25 3.75 3.75 — — — Expected average long-term rate of return on assets 6.96 6.39 6.39 5.00 4.10 4.10 (a)
Projected Benefit Payments for the Pension and Postretirement Benefit Plans	Projected Benefit Payments SPS’ projected benefit payments: (Millions of Dollars) Projected Net Projected Postretirement Health Care Benefit Payments (a) 2024 $ 36 $ 2 2025 29 2 2026 30 2 2027 31 2 2028 32 2 2029-2033 157 10 (a) Amount is reported net of expected Medicare Part D subsidies, which are immaterial.
Other Postretirement Benefits Plan [Member]
Benefit Plans and Other Postretirement Benefits [Abstract]
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost	Pension Benefits Postretirement Benefits (Millions of Dollars) 2023 2022 2023 2022 Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost: Net loss (gain) $ 155 $ 145 $ (20) $ (21) Prior service credit (1) (1) — — Total $ 154 $ 144 $ (20) $ (21) 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 $ 2 $ 2 $ — $ — Noncurrent regulatory assets 152 142 — — Current regulatory liabilities — — (1) (1) Noncurrent regulatory liabilities — — (19) (20) Total $ 154 $ 144 $ (20) $ (21) Measurement date Dec. 31, 2023 Dec. 31, 2022 Dec. 31, 2023 Dec. 31, 2022

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Asset Retirement Obligations	2023 (Millions of Dollars) Jan. 1, 2023 Accretion Dec. 31, 2023 Electric Steam and other production $ 83 $ 4 $ 87 Wind 54 2 56 Distribution 10 — 10 Total liability $ 147 $ 6 $ 153 2022 (Millions of Dollars) Jan. 1, 2022 Accretion Cash Flow Revisions (a) Dec. 31, 2022 Electric Steam and other production $ 54 $ 3 $ 26 $ 83 Wind 52 2 — 54 Distribution 10 — — 10 Total liability $ 116 $ 5 $ 26 $ 147 (a)
Assets and Liabilities, Lessee [Table Text Block]	Operating lease ROU assets: (Millions of Dollars) Dec. 31, 2023 Dec. 31, 2022 PPAs $ 500 $ 500 Other 44 44 Gross operating lease ROU assets 544 544 Accumulated amortization (141) (110) Net operating lease ROU assets $ 403 $ 434
Lease, Cost [Table Text Block]	Components of lease expense: (Millions of Dollars) 2023 2022 2021 Operating leases PPA capacity payments $ 53 $ 53 $ 53 Other operating leases (a) 4 4 4 Total operating lease expense (b) $ 57 $ 57 $ 57 (a) Includes immaterial short-term lease expense for 2023, 2022 and 2021. (b)
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	Commitments under operating leases as of Dec. 31, 2023: (Millions of Dollars) PPA (a) (b) Operating Leases Other Operating Leases Total Leases 2024 $ 46 $ 3 $ 49 2025 46 3 49 2026 46 3 49 2027 46 4 50 2028 46 4 50 Thereafter 220 33 253 Total minimum obligation 450 50 500 Interest component of obligation (85) (12) (97) Present value of minimum obligation 365 38 403 Less current portion (32) Noncurrent operating and finance lease liabilities $ 371 Weighted-average remaining lease term in years 10 (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.	[1]
Estimated Future Payments for Capacity and Energy Pursuant to Purchased Power Agreements	At Dec. 31, 2023, the estimated future payments for capacity and energy that SPS is obligated to purchase pursuant to these executory contracts, subject to availability, were as follows: (Millions of Dollars) Capacity Energy (a) 2024 $ 14 $ 33 2025 16 40 2026 16 38 2027 — — 2028 — — Thereafter — — Total $ 46 $ 111 (a) Excludes contingent energy payments for renewable energy PPAs.
Estimated Minimum Purchases Under Fuel Contracts	Estimated minimum purchases under these contracts as of Dec. 31, 2023: (Millions of Dollars) Coal Natural gas Natural gas 2024 $ 86 $ 21 $ 33 2025 20 — 29 2026 20 — 24 2027 20 — 24 2028 20 — 17 Thereafter — — 6 Total $ 166 $ 21 $ 133
[1] Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs.

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	Significant affiliate transactions among the companies and related parties for the years ended Dec. 31: (Millions of Dollars) 2023 2022 2021 Operating expenses: Other operating expenses — paid to Xcel Energy Services Inc. $ 245 $ 238 $ 209 Interest expense 4 1 — Accounts receivable and payable with affiliates at Dec. 31 were: 2023 2022 (Millions of Dollars) Accounts Receivable Accounts Payable Accounts Receivable Accounts Payable NSP-Minnesota $ 4 $ — $ 3 $ — PSCo 11 — 11 — Other subsidiaries of Xcel Energy Inc. 11 7 1 23 $ 26 $ 7 $ 15 $ 23

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Depreciation expense expressed as a percentage of average depreciable property	3.40%	3.40%	3.30%
Accounts and Financing Receivable, after Allowance for Credit Loss, Current and Noncurrent [Abstract]
Accounts Receivable, Allowance for Credit Loss, Current	$ 15	$ 13
Alternative Revenue Programs [Abstract]
maximum number of months following end of annual period	24 months
Public Utilities, Inventory [Line Items]
Inventory	$ 69	61
maximum number of months following end of annual period	24 months
Maturity period	3 months
Supplies
Public Utilities, Inventory [Line Items]
Inventory	$ 56	42
Fuel
Public Utilities, Inventory [Line Items]
Inventory	$ 13	$ 19

Property Plant and Equipment _3

Property Plant and Equipment Property Plant and Equipment (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property, plant and equipment		$ 11,226	$ 10,615
Accumulated Depreciation		(2,690)	(2,486)
Property, plant and equipment, net		8,536	8,129
Electric plant
Property, Plant and Equipment [Line Items]
Property, plant and equipment		10,752	10,182
Plant to be Retired [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	[1]	248	266
CWIP
Property, Plant and Equipment [Line Items]
Property, plant and equipment		$ 226	$ 167
[1] Amounts include Tolk Unit 1 and 2 and coal generation assets at Harrington pending facility gas conversion. Amounts are reported net of accumulated depreciation.

Regulatory Assets and Liabili_3

Regulatory Assets and Liabilities, Regulatory Assets (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Regulatory Assets [Line Items]
Regulatory Asset, Current		$ 30	$ 217
Regulatory Asset, Noncurrent		349	359
Regulatory assets not currently earning a return		123	48
Pension and Retiree Medical Obligations
Regulatory Assets [Line Items]
Regulatory Asset, Current		2	2	[1]
Regulatory Asset, Noncurrent		147	146	[1]
Excess deferred taxes - TCJA
Regulatory Assets [Line Items]
Regulatory Asset, Current		1	1	[1]
Regulatory Asset, Noncurrent		47	48	[1]
Recoverable Deferred Taxes on AFUDC Recorded in Plant
Regulatory Assets [Line Items]
Regulatory Asset, Current		0	0	[1]
Regulatory Asset, Noncurrent		44	40	[1]
Net AROs
Regulatory Assets [Line Items]
Regulatory Asset, Current	[2]	0	0	[1]
Regulatory Asset, Noncurrent	[2]	59	48	[1]
Losses on Reacquired Debt
Regulatory Assets [Line Items]
Regulatory Asset, Current		1	1	[1]
Regulatory Asset, Noncurrent		18	19	[1]
Deferred Fuel Costs
Regulatory Assets [Line Items]
Regulatory Asset, Current		0	136	[1]
Regulatory Asset, Noncurrent		0	34	[1]
Other
Regulatory Assets [Line Items]
Regulatory Asset, Current		26	77	[1]
Regulatory Asset, Noncurrent		$ 34	$ 24	[1]
[1] Prior period amounts have been restated to conform with current year presentation. Includes amounts recorded for future recovery of AROs.

Regulatory Assets and Liabili_4

Regulatory Assets and Liabilities, Regulatory Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		$ 116	$ 148
Regulatory Liability, Noncurrent		761	715
Regulatory assets not currently earning a return		123	48
Deferred Income Tax Adjustments and TCJA Refunds
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[1]	0	0	[2]
Regulatory Liability, Noncurrent	[1]	458	469	[2]
Plant Removal Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		0	0	[2]
Regulatory Liability, Noncurrent		$ 223	198	[2]
Deferred Electric Energy Costs | Maximum [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Amortization Period		1 year
Contract Valuation Adjustments
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[3]	$ 41	119	[2]
Regulatory Liability, Noncurrent	[3]	$ 0	1	[2]
Contract Valuation Adjustments | Maximum [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Amortization Period		1 year
Other
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		$ 14	19	[2]
Regulatory Liability, Noncurrent		10	5	[2]
Effect of regulation on employee benefit costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		0	0	[2]
Regulatory Liability, Noncurrent		19	20	[2]
Renewable resources and environmental initiatives
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		0	0	[2]
Regulatory Liability, Noncurrent		8	14	[2]
Formula rates
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		13	10	[2]
Regulatory Liability, Noncurrent		$ 10	8	[2]
Formula rates | Minimum [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Amortization Period		1 year
Formula rates | Maximum [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Amortization Period		2 years
Deferred Fuel Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		$ 15	0	[2]
Regulatory Liability, Noncurrent		0	0	[2]
LP&L Departure Payment
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		33	0	[2]
Regulatory Liability, Noncurrent		$ 33	$ 0	[2]
LP&L Departure Payment | Maximum [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Amortization Period		10 years
[1] Includes the revaluation of recoverable/regulated plant accumulated deferred income taxes and revaluation impact of non-plant accumulated deferred income taxes due to the TCJA. Prior period amounts have been reclassified to conform with current year presentation. Includes the fair value of FTR instruments utilized/intended to offset the impacts of transmission system congestion.

Short-Term Borrowings (Details)

Short-Term Borrowings (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Short-term Debt [Line Items]
Amount outstanding at period end	$ 75	$ 75	$ 34
Money Pool
Short-term Debt [Line Items]
Borrowing limit	100	100	100	$ 100
Amount outstanding at period end	27	27	0	91
Average amount outstanding	14	46	35	51
Maximum amount outstanding	$ 44	$ 100	$ 100	$ 100
Weighted average interest rate, computed on a daily basis (percentage)	5.34%	5.04%	0.44%	0.05%
Line of Credit Facility, Interest Rate at Period End	5.34%	5.34%		0.05%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 500	$ 500	$ 500	$ 500
Amount outstanding at period end	75	75	34	137
Average amount outstanding	18	50	100	63
Maximum amount outstanding	$ 95	$ 119	$ 324	$ 342
Weighted average interest rate, computed on a daily basis (percentage)	5.54%	5.12%	0.79%	0.21%
Weighted average interest rate at period end (percentage)	5.56%	5.56%	4.55%	0.26%

Letters of Credit (Details)

Letters of Credit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 75	$ 34
Letter of Credit
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 0	$ 2
Letter of Credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Period	1 year

Credit Facility (Details)

Credit Facility (Details) - Credit Facility $ in Millions		12 Months Ended
		Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Line of Credit Facility [Line Items]
Line Of Credit Facility Debt To Total Capitalization Ratio	[1]	46.10%	45.70%
Line Of Credit Facility Maximum Amount Credit Facility May Be Increased		$ 50
Number Of Additional Periods Revolving Termination Date Can Be Extended Subject To Majority Bank Group Approval	[2]	2
Line Of Credit Facility Maximum Debt To Total Capitalization Ratio Allowed		65%
Line Of Credit Facility Minimum Threshhold Percentage Of Subsidiary Assets To Consolidated Assets Required To Initiate Cross Default Provisions		15%
Line of Credit Facility, Minimum Amount of Indebtedness in Default to Initiate Cross Default Provisions		$ 75
Direct advances on the credit outstanding		0	$ 0
SPS [Member]
Line of Credit Facility [Line Items]
Credit facility	[3]	500
Drawn	[4]	75
Available		$ 425
[1] The credit facility has a financial covenant requiring that the debt-to-total capitalization ratio be less than or equal to 65%. All extension requests are subject to majority bank group approval. This credit facility matures in September 2027. Includes letters of credit and outstanding commercial paper.

Long-Term Borrowings (Details)

Long-Term Borrowings (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount (Premium), Net		$ (10)	$ (10)
Unamortized Debt Issuance Expense		(29)	(29)
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months		350
Long-term Debt, Maturities, Repayments of Principal in Year Two		0
Long-term Debt, Maturities, Repayments of Principal in Year Three		0
Long-term Debt, Maturities, Repayments of Principal in Year Four		0
Long-term Debt, Maturities, Repayments of Principal in Year Five		0
Deferred Finance Costs, Noncurrent, Net		29
Long-Term Debt, Current Maturities		(350)	0
Long-Term Debt		$ 2,961	3,211
First Mortgage Bonds, Series due: | Series Due June 15, 2024 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		3.30%
Face Amount		$ 150	150
First Mortgage Bonds, Series due: | Series Due June 15, 2024 2 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		3.30%
Face Amount		$ 200	200
First Mortgage Bonds, Series due: | Series Due Aug. 15, 2041 4
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		4.50%
Face Amount		$ 200	200
First Mortgage Bonds, Series due: | Series Due Aug. 15, 2041 2 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		4.50%
Face Amount		$ 100	100
First Mortgage Bonds, Series due: | Series Due Aug. 15, 2041 3 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		4.50%
Face Amount		$ 100	100
First Mortgage Bonds, Series due: | Series Due August 15, 2046 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		3.40%
Face Amount		$ 300	300
First Mortgage Bonds, Series due: | Series Due August 15, 2047 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		3.70%
Face Amount		$ 450	450
First Mortgage Bonds, Series due: | Series Due Nov. 15, 2048 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		4.40%
Face Amount		$ 300	300
First Mortgage Bonds, Series due: | Series Due June 15, 2049
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		3.75%
Face Amount		$ 300	300
First Mortgage Bonds, Series due: | Series due May 1, 2050 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		3.15%
Face Amount		$ 350	350
First Mortgage Bonds, Series due: | Series due May 1, 2050 2
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		3.15%
Face Amount		$ 250	250
First Mortgage Bonds, Series due: | Series Due June 1, 2052
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)	[1]	5.15%
Face Amount	[1]	$ 200	200
First Mortgage Bonds, Series due: | Series Due Sept. 15, 2053
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)	[2]	6%
Face Amount	[2]	$ 100	0
Unsecured Debt [Member] | Senior C and D Due Oct. 1, 2033 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		6%
Face Amount		$ 100	100
Unsecured Debt [Member] | Senior F Due Oct. 1, 2036 [Member]
Debt Instrument [Line Items]
Interest Rate, Stated Percentage (in hundredths)		6%
Face Amount		$ 250	$ 250
[1] 2022 financing.

Borrowings and Other Financin_3

Borrowings and Other Financing Instruments Preferred Stock (Details)	Dec. 31, 2023 $ / shares shares
Preferred Stock [Abstract]
Preferred Stock, Shares Authorized	10,000,000
Preferred Stock, Par or Stated Value Per Share | $ / shares	$ 1
Preferred Stock, Shares Outstanding	0

Borrowings and Other Financin_4

Borrowings and Other Financing Instruments Dividend and Other Restrictions (Details) $ in Millions	Dec. 31, 2023 USD ($)
Dividend and Other Restrictions [Abstract]
Equity to total capitalization ratio (excluding short-term debt), low end of range	45%
Equity to total capitalization ratio (excluding short-term debt), high end of range	55%
Equity to total capitalization ratio (excluding short-term debt)	54.60%	[1]
Unrestricted Retained Earnings Per State Regulatory Commissions Dividend Restrictions	$ 617
Capitalization, Short term debt, long term debt and equity	$ 7,298
[1] Excludes short-term debt.

Revenues (Details)

Revenues (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Customer Concentration Risk | Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage		10.60%
Regulated Electric | Retail
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers		$ 1,594	$ 1,598	$ 1,255
Regulated Electric | Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers		442	445	375
Regulated Electric | Retail | Commercial and Industrial Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	[1]	1,094	1,102	842
Regulated Electric | Retail | Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers		58	51	38
Regulated Electric | Wholesale
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers		223	407	873
Regulated Electric | Transmission
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers		296	296	287
Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers		0	10	6
Regulated Electric | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers		2,113	2,311	2,421
Regulated Electric | Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other		39	115	44
Total revenues | Regulated Electric
Disaggregation of Revenue [Line Items]
Total revenues		$ 2,152	$ 2,426	$ 2,465
[1] In 2023, revenues from one C&I customer represented approximately 10.6% of total revenues.

State Audits (Details)

State Audits (Details) $ in Millions	Dec. 31, 2023 USD ($)
Statement of Financial Position [Abstract]
state audits	$ 0

Unrealized Tax Benefits (Detail

Unrealized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2023	Jan. 01, 2022	Jan. 01, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Unrecognized tax benefit — Permanent tax positions	$ 5	$ 5
Reductions for tax positions of prior years	(5)	0	$ 0
NOL and tax credit carryforwards	(4)	(8)
Decrease in Unrecognized Tax Benefits is Reasonably Possible	2
Payable for interest related to unrecognized tax benefits	0	0	(1)				$ (1)
Unrecognized Tax Benefits, Interest on Income Taxes Expense	0	1	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0
Additions based on tax positions related to the current year	1	1	1
Unrecognized tax benefit — Temporary tax positions	0	4
Balance at Dec. 31	$ 5	$ 9	$ 8	$ 9	$ 8	$ 7

Other Income Tax Matters (Detai

Other Income Tax Matters (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
Income Tax [Line Items]
Federal NOL carryforward		$ 0	$ 8
Federal tax credit carryforwards		406	294
State NOL carryforwards		$ 3	$ 4
Federal statutory rate		21%	21%		21%
State income tax on pretax income, net of federal tax effect		2.40%	2.30%		2.50%
Effective Income Tax Rate Reconciliation, Tax Credit, Percent	[1]	(33.50%)	(35.90%)		(39.70%)
Plant regulatory differences (b)	[2]	(3.30%)	(3.80%)		(4.80%)
Amortization of deficient/(excess) nonplant deferred taxes		0.30%	(0.90%)		(1.10%)
Other, net		(0.20%)	(0.60%)		(0.70%)
Effective income tax rate		(13.30%)	(17.90%)		(22.80%)
Total income tax benefit		$ (45)	$ (53)		$ (59)
Deferred tax (benefit) expense excluding items below		(117)	37		(23)
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities		(16)	(20)		(24)
Total deferred tax assets		133	17		47
Tax credit carryforward		403
Tax Credit Carryforward, Valuation Allowance		(2)	0
income tax expense [Member]
Income Tax [Line Items]
Current federal tax expense (benefit)		76	(65)		(11)
Current state tax expense (benefit)		12	(5)		(1)
Deferred federal tax (benefit) expense		(132)	3		(57)
Deferred state tax (benefit) expense		(1)	13		9
Deferred change in unrecognized tax expense		0	1		1
Total income tax benefit		(45)	(53)		$ (59)
Net Deferred Tax Liablility [Member]
Income Tax [Line Items]
Federal tax credit carryforwards		406	294	[3]
Total deferred tax assets		623	467	[3]
Differences between book and tax bases of property		1,072	1,015	[3]
Operating lease assets		90	97	[3]
Regulatory assets		51	61	[3]
Total deferred tax liabilities		1,245	1,206	[3]
Regulatory liabilities		95	98	[3]
Deferred Fuel Cost		(5)	(35)	[3]
other employee benefits		6	6	[3]
Other		23	5	[3]
Net deferred tax liability		622	739	[3]
Operating lease liabilities		90	97	[3]
Operating Loss Carryforwards		0	2	[3]
Tax Credit Carryforward, Valuation Allowance		(2)	0	[3]
Deferred tax liability - Pension expense		$ 32	$ 33	[3]
[1] Wind PTCs net of estimated transfer discounts. Gross wind PTCs are credited to customers (reduction to revenue) and do not materially impact net income. Plant regulatory differences primarily relate to the credit of excess deferred taxes to customers through the average rate assumption method. Income tax benefits associated with the credit are offset by corresponding revenue reductions. Prior periods have been reclassified to conform to current year presentation.

Commodity Derivatives (Details)

Commodity Derivatives (Details) MWh in Millions, $ in Millions		Dec. 31, 2023 USD ($) MWh	Dec. 31, 2022 MWh
Electric Commodity [Member]
Derivative [Line Items]
Notional Amount | MWh	[1]	8	8
Interest Rate Swap
Derivative [Line Items]
Derivative Liability, Notional Amount | $		$ 0
[1] Not reflective of net positions in the underlying commodities.

Consideration of Credit Risk an

Consideration of Credit Risk and Concentrations (Details) - Credit Concentration Risk $ in Millions	Dec. 31, 2023 USD ($) Counterparty
Derivative [Line Items]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure	8
Municipal or Cooperative Entities or Other Utilities
Derivative [Line Items]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure	8
External Credit Rating, Investment Grade
Derivative [Line Items]
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 | $	$ 5
Percentage of wholesale, trading and non trading commodity credit exposure for the most significant counterparties	19%
External Credit Rating, Non Investment Grade
Derivative [Line Items]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure	1
Percentage of wholesale, trading and non trading commodity credit exposure for the most significant counterparties	1%
Internal Investment Grade
Derivative [Line Items]
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 | $	$ 23
Percentage of wholesale, trading and non trading commodity credit exposure for the most significant counterparties	81%

Impact of Derivative Activities

Impact of Derivative Activities on Income and Accumulated Other Comprehensive Loss (Details) - USD ($)		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Fair Value Hedges, Net		$ 0	$ 0	$ 0
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Instruments Gain (Loss) Reclassified To Regulatory Assets And Liabilities Net		(88,000,000)	(3,000,000)	28,000,000
Pre-tax gains (losses) reclassified into income during the period from regulatory assets and (liabilities)		78,000,000	2,000,000	(20,000,000)
Electric Commodity Contract | Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Instruments Gain (Loss) Reclassified To Regulatory Assets And Liabilities Net		(88,000,000)	(3,000,000)	28,000,000
Pre-tax gains (losses) reclassified into income during the period from regulatory assets and (liabilities)	[1]	$ (78,000,000)	$ (2,000,000)	$ 20,000,000
[1] 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.

Recurring Fair Value Measuremen

Recurring Fair Value Measurements (Details) - USD ($)		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Derivatives, Fair Value [Line Items]
Derivative Asset, Net		$ 0	$ 3,000,000
Derivative Liability, Current		2,000,000	4,000,000
Derivative Liability, Net		0	2,000,000
Return Cash Collateral		0	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Derivative Asset, Current		$ 42,000,000	$ 122,000,000
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]		Assets, Current	Assets, Current
Fair Value Hedges, Net		$ 0	$ 0	$ 0
Commodity Contract [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period		119,000,000	27,000,000	7,000,000
Purchases	[1]	79,000,000	248,000,000	10,000,000
Settlements	[1]	(89,000,000)	(168,000,000)	(79,000,000)
Gains (losses) recognized as regulatory assets	[1]	(70,000,000)	12,000,000	89,000,000
Balance at end of period		39,000,000	119,000,000	$ 27,000,000
Fair Value Measured on a Recurring Basis
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Derivative Asset, Current		39,000,000	119,000,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Electric Commodity Contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Derivative Asset, Current		39,000,000	119,000,000
Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		39,000,000	119,000,000
Netting	[2]	0	0
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0	0
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0	0
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		39,000,000	119,000,000
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity Contract
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		39,000,000	119,000,000
Netting	[2]	0	0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity Contract | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0	0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity Contract | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0	0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity Contract | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		39,000,000	119,000,000
Fair Value, Measurements, Nonrecurring | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Asset, Net	[3]	0	3,000,000
Derivative Liability, Current	[3]	2,000,000	4,000,000
Derivative Liability, Net	[3]	0	2,000,000
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Derivative Asset, Current	[3]	$ 3,000,000	$ 3,000,000
[1] Relates primarily to FTR instruments administered by SPP. SPS nets derivative instruments and related collateral on its balance sheet when supported by a legally enforceable master netting agreement. At Dec. 31, 2023 and 2022, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. Counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements. SPS currently applies the normal purchase exception to qualifying PPAs. Balance relates to specific contracts that were previously recognized at fair value prior to applying the normal purchase exception, and are being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

Fair Value of Long-Term Debt (D

Fair Value of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt, Gross	$ 3,311	$ 3,211
Long-term debt, Fair Value	$ 2,818	$ 2,674

Benefit Plans and Other Postr_3

Benefit Plans and Other Postretirement Benefits, Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2024	Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021
Pension Plan [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets			$ 420	[1]	$ 417	[1]	$ 557
Total benefit obligation			425		414		545
Net benefit cost recognized for financial reporting			$ 4		$ 6		$ 10
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets			6.96%		6.39%		6.39%
Pension Plan [Member] | Forecast [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets For Next Fiscal Year		6.97%
Pension Plan [Member] | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		$ 115		$ 172
Pension Plan [Member] | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		114		116
Pension Plan [Member] | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		1		0
Pension Plan [Member] | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		190		129
Pension Plan [Member] | Cash equivalents
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		38		21
Pension Plan [Member] | Cash equivalents | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		38		21
Pension Plan [Member] | Cash equivalents | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Pension Plan [Member] | Cash equivalents | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Pension Plan [Member] | Cash equivalents | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		0		0
Pension Plan [Member] | Commingled funds
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		262		273
Pension Plan [Member] | Commingled funds | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		72		144
Pension Plan [Member] | Commingled funds | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Pension Plan [Member] | Commingled funds | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Pension Plan [Member] | Commingled funds | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		190		129
Pension Plan [Member] | Debt securities
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		117		115
Pension Plan [Member] | Debt securities | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Pension Plan [Member] | Debt securities | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		116		115
Pension Plan [Member] | Debt securities | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		1		0
Pension Plan [Member] | Debt securities | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		0		0
Pension Plan [Member] | Equity securities
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		5		7
Pension Plan [Member] | Equity securities | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		5		7
Pension Plan [Member] | Equity securities | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Pension Plan [Member] | Equity securities | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Pension Plan [Member] | Equity securities | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		0		0
Pension Plan [Member] | Other Investments [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		(2)		1
Pension Plan [Member] | Other Investments [Member] | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Pension Plan [Member] | Other Investments [Member] | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		(2)		1
Pension Plan [Member] | Other Investments [Member] | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Pension Plan [Member] | Other Investments [Member] | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		0		0
Other Postretirement Benefits Plan [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets			36	[1]	36	[1]	$ 43
Total benefit obligation			26		26		34
Net benefit cost recognized for financial reporting			$ 1		$ 0		$ (1)
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets			5%		4.10%		4.10%
Other Postretirement Benefits Plan [Member] | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		$ 5		$ 8
Other Postretirement Benefits Plan [Member] | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		24		22
Other Postretirement Benefits Plan [Member] | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Other Postretirement Benefits Plan [Member] | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		7		6
Other Postretirement Benefits Plan [Member] | Cash equivalents
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		3		3
Other Postretirement Benefits Plan [Member] | Cash equivalents | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		3		3
Other Postretirement Benefits Plan [Member] | Cash equivalents | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Other Postretirement Benefits Plan [Member] | Cash equivalents | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Other Postretirement Benefits Plan [Member] | Cash equivalents | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		0		0
Other Postretirement Benefits Plan [Member] | Insurance contracts
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		5		4
Other Postretirement Benefits Plan [Member] | Insurance contracts | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Other Postretirement Benefits Plan [Member] | Insurance contracts | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		5		4
Other Postretirement Benefits Plan [Member] | Insurance contracts | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Other Postretirement Benefits Plan [Member] | Insurance contracts | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		0		0
Other Postretirement Benefits Plan [Member] | Commingled funds
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		9		11
Other Postretirement Benefits Plan [Member] | Commingled funds | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		2		5
Other Postretirement Benefits Plan [Member] | Commingled funds | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Other Postretirement Benefits Plan [Member] | Commingled funds | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Other Postretirement Benefits Plan [Member] | Commingled funds | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		7		6
Other Postretirement Benefits Plan [Member] | Debt securities
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		19		18
Other Postretirement Benefits Plan [Member] | Debt securities | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Other Postretirement Benefits Plan [Member] | Debt securities | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		19		18
Other Postretirement Benefits Plan [Member] | Debt securities | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]		0		0
Other Postretirement Benefits Plan [Member] | Debt securities | Fair Value Measured at Net Asset Value Per Share
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Plan asset investments measured at net asset value	[1]		0		0
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Net benefit cost recognized for financial reporting			2		17
Supplemental Executive Retirement Plan (SERP) and Nonqualified Pension Plan | Parent Company [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Total benefit obligation			$ 12		$ 11
[1] See Note 8 for further information on fair value measurement inputs and methods.

Benefit Plans and Other Postr_4

Benefit Plans and Other Postretirement Benefits, Pension Plan Benefit Obligations, Cash Flows and Benefit Costs (Details)		12 Months Ended
		Dec. 31, 2023 USD ($) Plan		Dec. 31, 2022 USD ($)		Dec. 31, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Operating and maintenance expenses		$ 279,000,000		$ 317,000,000		$ 271,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Liability, Defined Benefit Plan, Noncurrent		$ (12,000,000)		$ (12,000,000)
Significant Assumptions Used to Measure Costs [Abstract]
annual interest crediting rates		4.45		4.69		2.35
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Payment for Settlement				$ 2,000,000
Accumulated Benefit Obligation at Dec. 31		$ 395,000,000		386,000,000
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		414,000,000		545,000,000
Service cost		7,000,000		10,000,000		$ 11,000,000
Interest cost		22,000,000		16,000,000		15,000,000
Actuarial loss		16,000,000		(123,000,000)
Benefit payments		(34,000,000)		(34,000,000)
Obligation at Dec. 31		425,000,000		414,000,000		545,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		417,000,000	[1]	557,000,000
Actual return on plan assets		37,000,000		(106,000,000)
Benefit payments		(34,000,000)		(34,000,000)
Fair value of plan assets at Dec. 31		420,000,000	[1]	417,000,000	[1]	557,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		(5,000,000)		3,000,000
Liability, Defined Benefit Plan, Noncurrent		(6,000,000)		(4,000,000)
Assets for Plan Benefits, Defined Benefit Plan		1,000,000		7,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss		155,000,000		145,000,000
Prior service credit		(1,000,000)		(1,000,000)
Total		154,000,000		144,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory assets		2,000,000		2,000,000
Noncurrent regulatory assets		152,000,000		142,000,000
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Liabilities		0		0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Liabilities		0		0
Total		$ 154,000,000		$ 144,000,000
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		5.49%		5.80%
Expected average long-term increase in compensation level (as a percent)		4.25%		4.25%
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 7,000,000		$ 10,000,000		11,000,000
Interest cost		22,000,000		16,000,000		15,000,000
Expected return on plan assets		(32,000,000)		(31,000,000)		(30,000,000)
Amortization of net loss		2,000,000		10,000,000		14,000,000
Net periodic pension cost		(1,000,000)		7,000,000		10,000,000
Net benefit cost recognized for financial reporting		$ 4,000,000		$ 6,000,000		$ 10,000,000
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)		5.80%		3.08%		2.71%
Expected average long-term increase in compensation level (as a percent)		4.25%		3.75%		3.75%
Expected average long-term rate of return on assets (as a percent)		6.96%		6.39%		6.39%
Plan participant's contributions		$ 0		$ 0
Plan participant's contributions		0		0
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position		(5,000,000)		3,000,000
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[2]	0		2,000,000		$ 0
Defined Benefit Plan, Costs Not Recognized Due To Regulation		5,000,000		(1,000,000)		0
Pension Plan [Member] | SPS [Member]
Cash Flows [Abstract]
Payment for Pension Benefits						15,000,000
Other Postretirement Benefits Plan [Member]
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		26,000,000		34,000,000
Service cost		1,000,000		1,000,000		1,000,000
Interest cost		1,000,000		1,000,000		1,000,000
Actuarial loss		1,000,000		(8,000,000)
Benefit payments		(4,000,000)		(3,000,000)
Obligation at Dec. 31		26,000,000		26,000,000		34,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		36,000,000	[1]	43,000,000
Actual return on plan assets		3,000,000		(5,000,000)
Benefit payments		(4,000,000)		(3,000,000)
Fair value of plan assets at Dec. 31		36,000,000	[1]	36,000,000	[1]	43,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		10,000,000		10,000,000
Liability, Defined Benefit Plan, Noncurrent		0		0
Assets for Plan Benefits, Defined Benefit Plan		10,000,000		10,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss		(20,000,000)		(21,000,000)
Prior service credit		0		0
Total		(20,000,000)		(21,000,000)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory assets		0		0
Noncurrent regulatory assets		0		0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Liabilities		(1,000,000)		(1,000,000)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Liabilities		(19,000,000)		(20,000,000)
Total		$ (20,000,000)		$ (21,000,000)
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		5.54%		5.80%
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 1,000,000		$ 1,000,000		1,000,000
Interest cost		1,000,000		1,000,000		1,000,000
Expected return on plan assets		(1,000,000)		(2,000,000)		(2,000,000)
Amortization of net loss		0		0		(1,000,000)
Net periodic pension cost		1,000,000		0		(1,000,000)
Net benefit cost recognized for financial reporting		$ 1,000,000		$ 0		$ (1,000,000)
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)		5.80%		3.09%		2.65%
Expected average long-term increase in compensation level (as a percent)		0%		0%		0%
Expected average long-term rate of return on assets (as a percent)		5%		4.10%		4.10%
Plan participant's contributions		$ 1,000,000		$ 1,000,000
Plan participant's contributions		1,000,000		1,000,000
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position		$ 10,000,000		$ 10,000,000
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65		6.50%		6.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65		5.50%		5.50%
Ultimate health care trend assumption rate (as a percent)		4.50%		4.50%
Period until ultimate trend rate is reached (in years)		$ 6		$ 7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[2]	0		0		$ 0
Defined Benefit Plan, Costs Not Recognized Due To Regulation		$ 0		$ 0		$ 0
Parent Company [Member] | Pension Plan [Member]
Cash Flows [Abstract]
Number of pension plans to which contributions were made | Plan		4
[1] See Note 8 for further information on fair value measurement inputs and methods.

Benefit Plans and Other Postr_5

Benefit Plans and Other Postretirement Benefits, Postretirement Health Care Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Postretirement Health Care Benefits [Abstract]
Estimated costs of health plan subsidies - VRP	$ 1,000,000
Estimated cost of other medical benefits - VRP		$ 0
Other Postretirement Benefits Plan [Member]
Postretirement Health Care Benefits [Abstract]
Discount rate for year-end valuation (as a percent)	5.54%	5.80%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65	6.50%	6.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65	5.50%	5.50%
Ultimate health care trend assumption rate (as a percent)	4.50%	4.50%
Period until ultimate trend rate is reached (in years)	$ 6	$ 7
Total benefit obligation	$ 26,000,000	$ 26,000,000	$ 34,000,000
Target pension asset allocations (as a percent)	100%	100%
Other Postretirement Benefits Plan [Member] | Equity securities
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	9%	16%
Other Postretirement Benefits Plan [Member] | Long-Duration Fixed Income and Long-duration fixed income and interest rate swap securities
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	0%	0%
Other Postretirement Benefits Plan [Member] | Short-to-intermediate fixed income securities
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	77%	71%
Other Postretirement Benefits Plan [Member] | Alternative investments
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	13%	12%
Other Postretirement Benefits Plan [Member] | Cash
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	1%	1%
Pension Plan [Member]
Postretirement Health Care Benefits [Abstract]
Discount rate for year-end valuation (as a percent)	5.49%	5.80%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	4.25%	4.25%
Total benefit obligation	$ 425,000,000	$ 414,000,000	$ 545,000,000
Target pension asset allocations (as a percent)	100%	100%
Pension Plan [Member] | Equity securities
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	31%	33%
Pension Plan [Member] | Long-Duration Fixed Income and Long-duration fixed income and interest rate swap securities
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	38%	38%
Pension Plan [Member] | Short-to-intermediate fixed income securities
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	9%	9%
Pension Plan [Member] | Alternative investments
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	20%	18%
Pension Plan [Member] | Cash
Postretirement Health Care Benefits [Abstract]
Target pension asset allocations (as a percent)	2%	2%

Benefit Plans and Other Postr_6

Benefit Plans and Other Postretirement Benefits, Fair Value of Postretirement Benefit Plan Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Operating and maintenance expenses		$ 279		$ 317		$ 271
Other Postretirement Benefits Plan [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets		36	[1]	36	[1]	43
Other Postretirement Benefits Plan [Member] | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	5		8
Other Postretirement Benefits Plan [Member] | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	24		22
Other Postretirement Benefits Plan [Member] | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Other Postretirement Benefits Plan [Member] | Cash equivalents
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	3		3
Other Postretirement Benefits Plan [Member] | Cash equivalents | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	3		3
Other Postretirement Benefits Plan [Member] | Cash equivalents | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Other Postretirement Benefits Plan [Member] | Cash equivalents | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Other Postretirement Benefits Plan [Member] | Commingled funds
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	9		11
Other Postretirement Benefits Plan [Member] | Commingled funds | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	2		5
Other Postretirement Benefits Plan [Member] | Commingled funds | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Other Postretirement Benefits Plan [Member] | Commingled funds | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Other Postretirement Benefits Plan [Member] | Insurance contracts
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	5		4
Other Postretirement Benefits Plan [Member] | Insurance contracts | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Other Postretirement Benefits Plan [Member] | Insurance contracts | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	5		4
Other Postretirement Benefits Plan [Member] | Insurance contracts | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Other Postretirement Benefits Plan [Member] | Debt securities
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	19		18
Other Postretirement Benefits Plan [Member] | Debt securities | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Other Postretirement Benefits Plan [Member] | Debt securities | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	19		18
Other Postretirement Benefits Plan [Member] | Debt securities | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member]
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets		420	[1]	417	[1]	$ 557
Defined Benefit Plan, Plan Assets, Payment for Settlement				2
Pension Plan [Member] | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	115		172
Pension Plan [Member] | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	114		116
Pension Plan [Member] | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	1		0
Pension Plan [Member] | Cash equivalents
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	38		21
Pension Plan [Member] | Cash equivalents | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	38		21
Pension Plan [Member] | Cash equivalents | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Cash equivalents | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Commingled funds
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	262		273
Pension Plan [Member] | Commingled funds | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	72		144
Pension Plan [Member] | Commingled funds | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Commingled funds | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Debt securities
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	117		115
Pension Plan [Member] | Debt securities | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Debt securities | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	116		115
Pension Plan [Member] | Debt securities | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	1		0
Pension Plan [Member] | Equity securities
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	5		7
Pension Plan [Member] | Equity securities | Level 1
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	5		7
Pension Plan [Member] | Equity securities | Level 2
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	0		0
Pension Plan [Member] | Equity securities | Level 3
Plan Assets Measured at Fair Value for Each of the Fair Value Hierarchy Levels [Abstract]
Fair value of plan assets	[1]	$ 0		$ 0
[1] See Note 8 for further information on fair value measurement inputs and methods.

Benefit Plans and Other Postr_7

Benefit Plans and Other Postretirement Benefits, Postretirement Benefit Plan Benefit Obligations, Cash Flows and Benefit Costs (Details) - USD ($)		12 Months Ended
		Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Operating and maintenance expenses		$ 279,000,000		$ 317,000,000		$ 271,000,000
Other Postretirement Benefits Plan [Member]
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		26,000,000		34,000,000
Service cost		1,000,000		1,000,000		1,000,000
Interest cost		1,000,000		1,000,000		1,000,000
Plan participant's contributions		1,000,000		1,000,000
Actuarial loss		1,000,000		(8,000,000)
Benefit payments		(4,000,000)		(3,000,000)
Obligation at Dec. 31		26,000,000		26,000,000		34,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		36,000,000	[1]	43,000,000
Actual return on plan assets		3,000,000		(5,000,000)
Plan participant's contributions		1,000,000		1,000,000
Benefit payments		(4,000,000)		(3,000,000)
Fair value of plan assets at Dec. 31		36,000,000	[1]	36,000,000	[1]	43,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		10,000,000		10,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss		(20,000,000)		(21,000,000)
Prior service credit		0		0
Total		(20,000,000)		(21,000,000)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost (Credit) Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		0		0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Assets		0		0
Current regulatory liabilities		(1,000,000)		(1,000,000)
Noncurrent regulatory liabilities		(19,000,000)		(20,000,000)
Total		$ (20,000,000)		$ (21,000,000)
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		5.54%		5.80%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65		6.50%		6.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65		5.50%		5.50%
Ultimate health care trend assumption rate (as a percent)		4.50%		4.50%
Period until ultimate trend rate is reached (in years)		$ 6		$ 7
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		1,000,000		1,000,000		1,000,000
Interest cost		1,000,000		1,000,000		1,000,000
Expected return on plan assets		(1,000,000)		(2,000,000)		(2,000,000)
Amortization of net loss		0		0		(1,000,000)
Settlement charge (a)	[2]	0		0		0
Net periodic pension cost		1,000,000		0		(1,000,000)
Defined Benefit Plan, Costs Not Recognized Due To Regulation		0		0		0
Net benefit cost recognized for financial reporting		$ 1,000,000		$ 0		$ (1,000,000)
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)		5.80%		3.09%		2.65%
Expected average long-term increase in compensation level (as a percent)		0%		0%		0%
Expected average long-term rate of return on assets (as a percent)		5%		4.10%		4.10%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate, VRP		0.0550
Defined Benefit Plan, Health Care Cost Trend Rate Assumed and Ultimate Trend Assumption, VRP		0.0700
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Payment for Settlement				$ 2,000,000
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1		$ 414,000,000		545,000,000
Service cost		7,000,000		10,000,000		$ 11,000,000
Interest cost		22,000,000		16,000,000		15,000,000
Plan participant's contributions		0		0
Actuarial loss		16,000,000		(123,000,000)
Benefit payments		(34,000,000)		(34,000,000)
Obligation at Dec. 31		425,000,000		414,000,000		545,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		417,000,000	[1]	557,000,000
Actual return on plan assets		37,000,000		(106,000,000)
Plan participant's contributions		0		0
Benefit payments		(34,000,000)		(34,000,000)
Fair value of plan assets at Dec. 31		420,000,000	[1]	417,000,000	[1]	557,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status		(5,000,000)		3,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss		155,000,000		145,000,000
Prior service credit		(1,000,000)		(1,000,000)
Total		154,000,000		144,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost (Credit) Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		2,000,000		2,000,000
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Assets		152,000,000		142,000,000
Current regulatory liabilities		0		0
Noncurrent regulatory liabilities		0		0
Total		$ 154,000,000		$ 144,000,000
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)		5.49%		5.80%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		4.25%		4.25%
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 7,000,000		$ 10,000,000		11,000,000
Interest cost		22,000,000		16,000,000		15,000,000
Expected return on plan assets		(32,000,000)		(31,000,000)		(30,000,000)
Amortization of net loss		2,000,000		10,000,000		14,000,000
Settlement charge (a)	[2]	0		(2,000,000)		0
Net periodic pension cost		(1,000,000)		7,000,000		10,000,000
Defined Benefit Plan, Costs Not Recognized Due To Regulation		(5,000,000)		1,000,000		0
Net benefit cost recognized for financial reporting		$ 4,000,000		$ 6,000,000		$ 10,000,000
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)		5.80%		3.08%		2.71%
Expected average long-term increase in compensation level (as a percent)		4.25%		3.75%		3.75%
Expected average long-term rate of return on assets (as a percent)		6.96%		6.39%		6.39%
[1] See Note 8 for further information on fair value measurement inputs and methods.

Net Periodic Benefit Cost (Deta

Net Periodic Benefit Cost (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Operating and maintenance expenses		$ 279	$ 317	$ 271
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		7	10	11
Interest cost		22	16	15
Defined Benefit Plan, Expected Return (Loss) on Plan Assets		(32)	(31)	(30)
Defined Benefit Plan, Amortization of Gain (Loss)		2	10	14
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[1]	0	2	0
Net periodic pension cost		(1)	7	10
Defined Benefit Plan, Costs Not Recognized Due To Regulation		5	(1)	0
Net benefit cost recognized for financial reporting		$ 4	$ 6	$ 10
Discount rate (as a percent)		5.80%	3.08%	2.71%
Expected average long-term increase in compensation level (as a percent)		4.25%	3.75%	3.75%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets		6.96%	6.39%	6.39%
Defined Benefit Plan, Plan Assets, Payment for Settlement			$ 2
Net loss		$ 155	145
Prior service credit		(1)	(1)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Total		154	144
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		2	2
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Assets		152	142
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Liabilities		0	0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Liabilities		0	0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		1	1	$ 1
Interest cost		1	1	1
Defined Benefit Plan, Expected Return (Loss) on Plan Assets		(1)	(2)	(2)
Defined Benefit Plan, Amortization of Gain (Loss)		0	0	(1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	[1]	0	0	0
Net periodic pension cost		1	0	(1)
Defined Benefit Plan, Costs Not Recognized Due To Regulation		0	0	0
Net benefit cost recognized for financial reporting		$ 1	$ 0	$ (1)
Discount rate (as a percent)		5.80%	3.09%	2.65%
Expected average long-term increase in compensation level (as a percent)		0%	0%	0%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets		5%	4.10%	4.10%
Net loss		$ (20)	$ (21)
Prior service credit		0	0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Total		(20)	(21)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Assets		0	0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Assets		0	0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Liabilities		(1)	(1)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Liabilities		$ (19)	$ (20)
[1]A settlement charge is required when the amount of all 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 2022, as a result of lump-sum distributions during each plan year, SPS recorded a total pension settlement charge of $2 million. An immaterial amount was recorded in the income statement in 2022. There were no settlement charges recorded to the qualified pension plans in 2023 or 2021.

Cash Flow (Details)

Cash Flow (Details) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2024 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($) Plan	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			100%	100%
Pension Plan [Member] | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			31%	33%
Pension Plan [Member] | Long-Duration Fixed Income and Long-duration fixed income and interest rate swap securities
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			38%	38%
Pension Plan [Member] | Short-to-intermediate fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			9%	9%
Pension Plan [Member] | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			20%	18%
Pension Plan [Member] | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			2%	2%
Pension Plan [Member] | Xcel Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits			$ 50	$ 50	$ 131
Pension Plan [Member] | SPS [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits					15
Pension Plan [Member] | Subsequent Event | Xcel Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits	$ 100
Defined Benefit Plan, Overfunded Plan [Member] | Xcel Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits			$ 11	$ 13	$ 15
Defined Benefit Plan, Overfunded Plan [Member] | Subsequent Event | Xcel Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits		$ 11
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			100%	100%
Other Postretirement Benefits Plan [Member] | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			9%	16%
Other Postretirement Benefits Plan [Member] | Long-Duration Fixed Income and Long-duration fixed income and interest rate swap securities
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			0%	0%
Other Postretirement Benefits Plan [Member] | Short-to-intermediate fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			77%	71%
Other Postretirement Benefits Plan [Member] | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			13%	12%
Other Postretirement Benefits Plan [Member] | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Target pension asset allocations (as a percent)			1%	1%
Parent Company [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan number of pension plans to which contributions were made | Plan			4

Plan Amendments (Details)

Plan Amendments (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021
Retirement Benefits [Abstract]
plan ammendments	$ 0	$ 0

Projected Benefit Payments (Det

Projected Benefit Payments (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Defined Contribution Plan, Administrative Expense			$ 4	$ 4	$ 4
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Accumulated Benefit Obligation			395	386
Defined Benefit Plan, Gross Projected Benefit Payments [Abstract]
2022			36
2023			29
2024			30
2025			31
2026			32
2027-2031			157
Pension Plan [Member] | Xcel Energy [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits			50	50	131
Pension Plan [Member] | Xcel Energy [Member] | Subsequent Event
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits	$ 100
Pension Plan [Member] | SPS [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits					15
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
2022			2
2023			2
2024			2
2025			2
2026			2
2027-2031			10
Defined Benefit Plan, Overfunded Plan [Member] | Xcel Energy [Member]
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits			$ 11	$ 13	$ 15
Defined Benefit Plan, Overfunded Plan [Member] | Xcel Energy [Member] | Subsequent Event
Defined Benefit Plan, Net Projected Benefit Payments [Abstract]
Payment for Pension Benefits		$ 11

Commitments and Contingencies S

Commitments and Contingencies SPP OATT Upgrade Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Southwest Power Pool (SPP) [Member] | SPP Open Access Transmission Tariff Upgrade Costs [Member] | SPS [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Billed Charges For Transmission Service Upgrades	$ 13

Commitment and Contingencies Wi

Commitment and Contingencies Wind Operating Commitments (Details)	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Wind operating commitments, minimum net capacity factor	48%

Commitments and Contingencies,

Commitments and Contingencies, Asset Retirement Obligations (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		$ 147	$ 116
Accretion		6	5
Ending balance		153	147
Cash flow revisions	[1]		26
Electric Plant Steam Production Asbestos
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		83	54
Accretion		4	3
Ending balance		87	83
Electric Plant Wind Production [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		54	52
Accretion		2	2
Ending balance		56	54
Cash flow revisions	[1]		0
Electric Plant Distribution
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		10	10
Accretion		0	0
Ending balance		$ 10	10
Cash flow revisions	[1]		$ 0
[1] In 2022, AROs were revised for changes in estimates of cash flows. Revisions in steam and other production AROs primarily related to changes in costs for steam production ponds remediation.

Indeterminate AROs (Details)

Indeterminate AROs (Details) $ in Millions	Dec. 31, 2023 USD ($)
Statement of Financial Position [Abstract]
Indeterminate Costs Incurred, Asset Retirement Obligation Due to Asbestos	$ 0

Commitments and Contingencies_2

Commitments and Contingencies, Leases (Details) - USD ($)		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Lessee, Lease, Description [Line Items]
Maximum Length - Short-Term Leases		12 months
Operating Lease, Weighted Average Discount Rate, Percent		4.40%
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross		$ 544,000,000	$ 544,000,000
Operating Lease, Right-of-Use Asset, Accumulated Depreciation		(141,000,000)	(110,000,000)
Operating lease right-of-use assets		403,000,000	434,000,000
Lease, Cost [Abstract]
Operating Lease, Cost	[1]	57,000,000	57,000,000	$ 57,000,000
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2024		49,000,000
2025		49,000,000
2026		49,000,000
2027		50,000,000
2028		50,000,000
Thereafter		253,000,000
Total minimum obligation		500,000,000
Interest component of obligation		(97,000,000)
Tax credit carryforward		403,000,000
Less current portion		(32,000,000)	(31,000,000)
Operating Lease, Liability, Noncurrent		371,000,000	403,000,000
Weighted Average Remaining lease term, operating		10
Property, Plant and Equipment, Other Types [Member]
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross		44,000,000	44,000,000
Lease, Cost [Abstract]
Operating Lease, Cost	[2]	4,000,000	4,000,000	4,000,000
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2024		3,000,000
2025		3,000,000
2026		3,000,000
2027		4,000,000
2028		4,000,000
Thereafter		33,000,000
Total minimum obligation		50,000,000
Interest component of obligation		(12,000,000)
Tax credit carryforward		38,000,000
Purchased Power Agreements
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross		500,000,000	500,000,000
Lease, Cost [Abstract]
Operating Lease, Cost		53,000,000	$ 53,000,000	$ 53,000,000
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2024	[3],[4]	46,000,000
2025	[3],[4]	46,000,000
2026	[3],[4]	46,000,000
2027	[3],[4]	46,000,000
2028	[3],[4]	46,000,000
Thereafter	[3],[4]	220,000,000
Total minimum obligation	[3],[4]	450,000,000
Interest component of obligation	[3],[4]	(85,000,000)
Tax credit carryforward	[3],[4]	$ 365,000,000
[1] 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. Includes immaterial short-term lease expense for 2023, 2022 and 2021. Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs. PPA operating leases contractually expire at various dates through 2033.

Commitments and Contingencies_3

Commitments and Contingencies, Purchased Power Agreements (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Estimated Future Payments Under PPAs [Abstract]
Minimum payments related to SPS' extension of non-lease PPA		$ 1,000
Capacity
Purchased Power Agreements (PPAs) [Abstract]
Payments for capacity		12	$ 12	$ 12
Estimated Future Payments Under PPAs [Abstract]
2024		14
2025		16
2026		16
2027		0
2028		0
Thereafter		0
Total		46
Energy Payments
Estimated Future Payments Under PPAs [Abstract]
2024	[1]	33
2025	[1]	40
2026	[1]	38
2027	[1]	0
2028	[1]	0
Thereafter	[1]	0
Total	[1]	$ 111
[1] Excludes contingent energy payments for renewable energy PPAs.

Commitments and Contingencies_4

Commitments and Contingencies, Fuel Contracts (Details) $ in Millions	Dec. 31, 2023 USD ($)
Coal
Fuel Contracts [Abstract]
2024	$ 86
2025	20
2026	20
2027	20
2028	20
Thereafter	0
Total	166
Natural Gas Supply [Member]
Fuel Contracts [Abstract]
2024	21
2025	0
2026	0
2027	0
2028	0
Thereafter	0
Total	21
Natural Gas Storage and Transportation [Member]
Fuel Contracts [Abstract]
2024	33
2025	29
2026	24
2027	24
2028	17
Thereafter	6
Total	$ 133

Commitments and Contingencies_5

Commitments and Contingencies, Variable Interest Entities (Details) - MW	Dec. 31, 2023	Dec. 31, 2022
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Purchased Power Agreements [Abstract]
Generating capacity (in MW)	1,197	1,197

Commitments and Contingencies -

Commitments and Contingencies - Historical MGP, Landfill, and Disposal Sites (Details) - Other MGP, Landfill, or Disposal Sites	Dec. 31, 2023 Site
Statement of Financial Position [Abstract]
Number of identified MGP, landfill, or disposal sites under current investigation and/or remediation	2
Loss Contingencies [Line Items]
Number of identified MGP, landfill, or disposal sites under current investigation and/or remediation	2

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
NSP-Minnesota
Operating expenses [Abstract]
Other Receivables	$ 4	$ 3
Accounts Payable, Other	0	0
PSCo
Operating expenses [Abstract]
Other Receivables	11	11
Accounts Payable, Other	0	0
Other Subsidiaries of Xcel Energy Inc.
Operating expenses [Abstract]
Other Receivables	11	1
Accounts Payable, Other	7	23
Xcel Energy [Member]
Operating expenses [Abstract]
Other Receivables	26	15
Accounts Payable, Other	7	23
Other Expense [Member]
Operating expenses [Abstract]
Costs and Expenses, Related Party	245	238	$ 209
Interest Expense
Operating expenses [Abstract]
Costs and Expenses, Related Party	$ 4	$ 1	$ 0

Compensation Related Costs, P_2

Compensation Related Costs, Postemployment Benefits (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) Employees
Xcel Energy [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other Postretirement Benefits Cost (Reversal of Cost) | $	$ 72
Xcel Energy [Member] | Voluntary Retirement Program
Postemployment Benefits [Abstract]
Entity Number of Employees	400
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Entity Number of Employees	400
Xcel Energy [Member] | Employee Severance
Postemployment Benefits [Abstract]
Entity Number of Employees	150
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Entity Number of Employees	150
SPS [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other Postretirement Benefits Cost (Reversal of Cost) | $	$ 9

Schedule II, Valuation and Qu_2

Schedule II, Valuation and Qualifying Accounts (Details) - Allowance for Bad Debts - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Jan. 1		$ 13	$ 12	$ 8
Charged to costs and expenses		11	9	6
Charged to other accounts	[1]	1	1	3
Deductions from reserves	[2]	(10)	(9)	(5)
Balance at Dec. 31		$ 15	$ 13	$ 12
[1] Recovery of amounts previously written-off.