Fair Value Disclosures [Abstract] Derivative [Table] Derivative [Table] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Derivative, by Nature [Axis] Derivative Instrument [Axis] Derivative, Name [Domain] Derivative Contract [Domain] Interest Rate Swap [Member] Interest Rate Swap [Member] Electric Commodity (in megawatt hours) Electric Commodity [Member] Derivative instrument whose primary underlying risk is tied to electric commodity prices. Concentration Risk by Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Credit Concentration Risk Credit Concentration Risk [Member] Credit Quality Indicator [Axis] Credit Quality Indicator [Axis] Information by credit quality indicator. Credit Quality Indicator [Domain] Credit Quality Indicator [Domain] Credit quality indicators related to credit exposure. External Credit Rating, Investment Grade [Member] External Credit Rating, Investment Grade [Member] No Investment Grade Ratings from External Credit Rating Agencies [Member] No Investment Grade Ratings from External Credit Rating Agencies [Member] Did not receive investment grade ratings by the external credit rating agencies Standard & Poors, Moody's or Fitch. Received credit quality rating consistent with investment grade based on internal analysis. External Credit Rating, Non Investment Grade [Member] External Credit Rating, Non Investment Grade [Member] Industry of Counterparty, Type [Axis] Industry of Counterparty, Type [Axis] Industry of Counterparty [Domain] Industry of Counterparty [Domain] Municipal or Cooperative Entities or Other Utilities [Member] Municipal or Cooperative Entities or Other Utilities [Member] Municipal or Cooperative Entities or Other Utilities [Member] Derivative [Line Items] Derivative [Line Items] Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Gross Notional Amounts of Commodity FTRs [Abstract] Gross Notional Amounts of Commodity Forwards and Options [Abstract] -- None. No documentation exists for this element. -- Derivative, Nonmonetary Notional amount Derivative, Nonmonetary Notional Amount Consideration of Credit Risk and Concentrations [Abstract] Consideration of Credit Risk and Concentrations [Abstract] -- None. No documentation exists for this element. -- Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure Number of the entity's most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure. Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties Wholesale, trading and non trading commodity credit exposure for the most significant counterparties Wholesale, trading and non-trading commodity credit exposure for the entity's most significant counterparties. Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths) Percentage of wholesale, trading and non trading commodity credit exposure for the most significant counterparties Percentage of wholesale, trading and non-trading commodity credit exposure for the entity's most significant counterparties. Income Tax Disclosure [Abstract] Income Tax Examination [Table] Income Tax Examination [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Internal Revenue Service (IRS) Internal Revenue Service (IRS) [Member] TEXAS TEXAS Income Tax Examination [Line Items] Income Tax Examination [Line Items] Tax Audits [Abstract] Tax Audits [Abstract] -- None. No documentation exists for this element. -- Year(s) under examination Tax years under examination The tax year(s) being audited in connection with the income tax examination. Tax years under examination, Concluded Tax years under examination, Concluded Tax years under examination, Concluded Earliest year subject to examination Earliest Open Tax Year Subject To Examination The earliest open tax year(s) subject to income tax examination by a taxing authority. Potential Tax Adjustments Potential Tax Adjustments The potential income tax expense that could become payable in the event of a successful challenge by a taxing authority of an entity's income tax position. Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent Regulatory differences - reversal of prior quarters' ARAM deferral (b) Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Effective Income Tax Rate Reconciliation, Percent Effective Income Tax Rate Reconciliation, Percent Unrecognized Tax Benefits [Abstract] Income Tax Uncertainties [Abstract] Unrecognized tax benefit - Permanent tax positions Unrecognized Tax Benefits that Would Impact Effective Tax Rate Unrecognized tax benefit - Temporary tax positions Unrecognized Tax Benefits That Would Not Impact Effective Tax Rate The total amount of unrecognized tax benefits for which the ultimate deductibility is highly certain but for which there is uncertainty about the timing of such deductibility and, if recognized, would not affect the effective tax rate but would accelerate the payment of cash to the taxing authority to an earlier period. Total unrecognized tax benefit Unrecognized Tax Benefits NOL and tax credit carryforwards Tax Benefits Associated With Nol And Tax Credit Carryforwards Tax benefits associated with NOL and tax credit carryforwards that reduce unrecognized tax benefits. Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards Upper bound of decrease in unrecognized tax benefit that is reasonably possible Decrease in Unrecognized Tax Benefits is Reasonably Possible Amounts accrued for penalties related to unrecognized tax benefits Unrecognized Tax Benefits, Income Tax Penalties Accrued Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Receivable for interest related to unrecognized tax benefits at beginning of period Unrecognized Tax Benefits, Interest on Income Taxes Accrued Interest income related to unrecognized tax benefits Unrecognized Tax Benefits, Interest on Income Taxes Expense Receivable for interest related to unrecognized tax benefits at end of period Debt Disclosure [Abstract] Borrowings and Other Financing Instruments Debt Disclosure [Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Credit Facility Revolving Credit Facility [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Credit Facility Line of Credit Facility, Maximum Borrowing Capacity Drawn Debt, Long-term and Short-term, Combined Amount Available Line of Credit Facility, Remaining Borrowing Capacity Direct advances on the credit facility outstanding Long-term Line of Credit Revenue from Contract with Customer [Abstract] Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Balance Sheet Related Disclosures [Abstract] Public Utility, Property, Plant and Equipment [Table] Public Utility, Property, Plant and Equipment [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Electric Generation Equipment [Member] Electric Generation Equipment [Member] Construction in Progress [Member] Construction in Progress [Member] Public Utility, Property, Plant and Equipment [Line Items] Public Utility, Property, Plant and Equipment [Line Items] Property, Plant and Equipment, Gross Property, Plant and Equipment, Gross Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property, Plant and Equipment, Net Property, Plant and Equipment, Net Stockholders' Equity Note [Abstract] New Accounting Pronouncements and Changes in Accounting Principles [Abstract] Accounting Pronouncements New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Accounting Policies [Abstract] Public Utilities, Inventory [Table] Public Utilities, Inventory [Table] Inventory [Axis] Inventory [Axis] Inventory [Domain] Inventory [Domain] Public Utilities, Inventory, Fuel [Member] Public Utilities, Inventory, Fuel [Member] Supplies [Member] Supplies [Member] Public Utilities, Inventory [Line Items] Public Utilities, Inventory [Line Items] Public Utilities, Inventory Public Utilities, Inventory Allowance for Doubtful Accounts Receivable, Current Allowance for Doubtful Accounts Receivable, Current Commitments and Contingencies Disclosure [Abstract] Loss Contingencies [Table] Loss Contingencies [Table] Loss Contingencies by Nature of Contingency [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock Common Stock [Member] Additional Paid In Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Statement [Line Items] Statement [Line Items] Common Stock, Dividends, Per Share, Declared Common Stock, Dividends, Per Share, Declared Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Balance (in shares) Common Stock, Shares, Outstanding Net income Net Income (Loss) Attributable to Parent Other comprehensive income Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Dividends declared on common stock Dividends, Common Stock Ending balance Balance (in shares) Inventory Disclosure [Abstract] Revenue Revenue from Contract with Customer [Text Block] Statement of Comprehensive Income [Abstract] Comprehensive income: Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Other comprehensive income Other Comprehensive Income (Loss), Net of Tax [Abstract] Derivative instruments: Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, Tax [Abstract] Reclassification of losses to net income, tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax Public Utilities, General Disclosures [Abstract] Public Utilities General Disclosures [Table] Public Utilities General Disclosures [Table] Environmental Remediation Site [Axis] Environmental Remediation Site [Axis] Environmental Remediation Site [Domain] Environmental Remediation Site [Domain] Other MGP, Landfill, or Disposal Sites [Domain] Other MGP, Landfill, or Disposal Sites [Domain] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] SPS SPS [Member] SPS is an operating utility engaged primarily in the generation, purchase, transmission, distribution and sale of electricity in portions of Texas and New Mexico. Regulatory Agency [Axis] Regulatory Agency [Axis] Regulatory Agency [Domain] Regulatory Agency [Domain] Southwest Power Pool (SPP) Southwest Power Pool (SPP) [Member] Southwest Power Pool (SPP) [Member] Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] SPP Open Access Transmission Tariff Upgrade Costs SPP Open Access Transmission Tariff Upgrade Costs [Member] SPP Open Access Transmission Tariff (OATT) Upgrade Costs Public Utilities, General Disclosures [Line Items] Public Utilities, General Disclosures [Line Items] Accrual for Environmental Loss Contingencies Accrual for Environmental Loss Contingencies Public Utilities, Billed Charges For Transmission Service Upgrades Public Utilities, Billed Charges For Transmission Service Upgrades Public Utilities, Billed Charges For Transmission Service Upgrades Public Utilities, Annual Transmission Revenue Requirement Increase Public Utilities, Annual Transmission Revenue Requirement Increase Public Utilities, Annual Transmission Revenue Requirement Increase Public Utilities, Annual Transmission Revenue Requirement Increase (SPS) Public Utilities, Annual Transmission Revenue Requirement Increase (SPS) Public Utilities, Annual Transmission Revenue Requirement Increase (SPS) Public Utilities, Annual Transmission Revenue Requirement (Other Utilities) Public Utilities, Annual Transmission Revenue Requirement (Other Utilities) Public Utilities, Annual Transmission Revenue Requirement (Other Utilities) Public Utilities, Amount proposed changes would increase wholesale transmission revenues Public Utilities, Amount proposed changes would increase wholesale transmission revenues Public Utilities, Amount proposed changes would increase wholesale transmission revenues Public Utilities, Amount of proposed changes would be recoverable Public Utilities, Amount of proposed changes would be recoverable Public Utilities, Amount of proposed changes would be recoverable Selected Balance Sheet Data Supplemental Balance Sheet Disclosures [Text Block] Schedule of Short-term Debt [Table] Schedule of Short-term Debt [Table] Short-term Debt, Type [Axis] Short-term Debt, Type [Axis] Short-term Debt, Type [Domain] Short-term Debt, Type [Domain] Money Pool Money Pool [Member] Arrangement that allows for short-term investments in and borrowings between the utility subsidiaries. Commercial Paper Commercial Paper [Member] Short-term Debt [Line Items] Short-term Debt [Line Items] Borrowing limit Amount outstanding at period end Short-term Debt Average amount outstanding Short-term Debt, Average Outstanding Amount Maximum amount outstanding Short-term Debt, Maximum Amount Outstanding During Period Weighted average interest rate, computed on a daily basis (percentage) Line of Credit Facility, Interest Rate During Period Weighted average interest rate at period end (percentage) Short-term Debt, Weighted Average Interest Rate, at Point in Time Statement of Financial Position [Abstract] Restatement [Axis] Restatement [Axis] Restatement [Domain] Restatement [Domain] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Assets Assets [Abstract] Current assets Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Accounts receivable, net Accounts Receivable, Net, Current Accounts receivable from affiliates Due from Affiliate, Current Accrued unbilled revenues Accrued Unbilled Revenues The amount of fees and other revenue, excluding investment income receivable, earned but not yet received, which were recognized in conformity with revenue recognition criteria based on estimates or specific contractual terms. Regulatory assets Regulatory Assets, Current Derivative instruments Derivative Instruments and Hedges, Assets Prepaid taxes Prepaid Taxes Prepayments and other Prepaid Expense and Other Assets, Current Total current assets Assets, Current Other assets Assets, Noncurrent [Abstract] Regulatory assets Regulatory Assets, Noncurrent Derivative instruments Derivative Instruments and Hedges, Noncurrent Operating Lease, Right-of-Use Asset Operating Lease, Right-of-Use Asset Other Other Assets, Noncurrent Total other assets Other Assets, Excluding Property, Plant and Equipment Sum of the carrying amounts as of the balance sheet date of all assets, excluding net property, plant and equipment, that are expected to be realized in cash, sold or consumed after one year or beyond the normal operating cycle, if longer. Total assets Assets Liabilities and Equity Liabilities and Equity [Abstract] Current liabilities Liabilities, Current [Abstract] Short-term debt Borrowings Payable Under Utility Money Pool Arrangement Borrowings Payable Under Utility Money Pool Arrangement Borrowings under the utility money pool borrowing arrangement among approved affiliates, which are due in one year or less in the future. Accounts payable Accounts Payable, Current Accounts payable to affiliates Due to Affiliate, Current Regulatory liabilities Regulatory Liability, Current Taxes accrued Taxes Payable, Current Accrued interest Interest Payable, Current Dividends payable Dividends Payable, Current Derivative instruments Derivative Instruments and Hedges, Liabilities Other Other Liabilities, Current Total current liabilities Liabilities, Current Deferred credits and other liabilities Liabilities, Other than Long-term Debt, Noncurrent [Abstract] Deferred income taxes Deferred Tax Liabilities, Net, Noncurrent Regulatory liabilities Regulatory Liability, Noncurrent Asset retirement obligations Asset Retirement Obligations, Noncurrent Derivative instruments Derivative Instruments and Hedges, Liabilities, Noncurrent Pension and employee benefit obligations Liability, Defined Benefit Plan, Noncurrent Noncurrent operating lease liabilities Operating Lease, Liability, Noncurrent Other Other Liabilities, Noncurrent Total deferred credits and other liabilities Liabilities, Other than Long-term Debt, Noncurrent Capitalization Capitalization, Long-term Debt and Equity [Abstract] Long-term debt Long-term Debt, Excluding Current Maturities Common stock — 200 shares authorized of $1.00 par value; 100 shares outstanding at March 31, 2019 and Dec. 31, 2018, respectively Common Stock, Value, Issued Additional paid in capital Additional Paid in Capital, Common Stock Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Total common stockholder’s equity Stockholders' Equity Attributable to Parent Total liabilities and equity Liabilities and Equity Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] PPAs Purchased Power Agreements [Member] Purchased Power Agreements [Member] Other Property, Plant and Equipment, Other Types [Member] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Maximum lease term for short-term lease classification Maximum lease term for short-term lease classification Maximum lease term for short-term lease classification Operating Lease, Right-of-Use Asset, Gross Operating Lease, Right-of-Use Asset, Gross Operating Lease, Right-of-Use Asset, Gross Operating Lease, Right-of-Use Asset, Accumulated Depreciation Operating Lease, Right-of-Use Asset, Accumulated Depreciation Operating Lease, Right-of-Use Asset, Accumulated Depreciation Operating Lease, Right-of-Use Asset Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Financial Liabilities, Balance Sheet Groupings [Abstract] Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Long-term debt, including current portion Debt Instrument, Fair Value Disclosure Document and Entity Information [Abstract] -- None. No documentation exists for this element. -- Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Document Type Document Type Entity Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Organization, Consolidation and Presentation of Financial Statements [Abstract] Management's Opinion Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Operating Lease, Cost Operating Lease, Cost Short-term Lease, Cost Short-term Lease, Cost Pension and retiree medical benefits: Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract] Derivative instruments: Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract] Reclassification of losses to net income, net of tax of $0 and $0, respectively Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Other comprehensive income Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-02 [Member] Accounting Standards Update 2016-02 [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Operating Lease, Liability Operating Lease, Liability Accounts receivable, net Accounts Receivable, Net, Current [Abstract] Accounts receivable Accounts Receivable, Gross, Current Less allowance for bad debts Accounts receivable, net Gross Notional Amounts of Commodity FTRs Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Derivative Assets and Liabilities Measured at Fair Value on a Recurring Basis by Hierarchy Level Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Changes in Level 3 Commodity Derivatives Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Table Text Block] Tabular disclosure of the fair value measurement of net assets and liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings or recognized in other comprehensive income, purchases, sales, issuances, and settlements, and transfers in and transfers out of Level 3. Carrying Amount and Fair Value of Long-term Debt Fair Value, by Balance Sheet Grouping [Table Text Block] Borrowings and Other Financing Instruments [Abstract] Debt Instruments [Abstract] Short-Term Borrowings Schedule of Short-term Debt [Table Text Block] Credit Facilities Schedule of Line of Credit Facilities [Table Text Block] Income Statement [Abstract] Revenues [Abstract] Revenues [Abstract] Operating revenues Revenues Operating expenses Costs and Expenses [Abstract] Electric fuel and purchased power Cost of Goods and Services Sold Operating and maintenance expenses Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses Demand side management expenses Conservation And Demand Side Management Program Expenses Costs incurred for energy conservation, weatherization and other programs to conserve or manage energy use by customers. Depreciation and amortization Utilities Operating Expense, Depreciation and Amortization Taxes (other than income taxes) Taxes, Miscellaneous Total operating expenses Costs and Expenses Operating income Operating Income (Loss) Other income (expense), net Other Nonoperating Income Allowance for funds used during construction — equity Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Interest charges and financing costs Interest and Debt Expense [Abstract] Interest charges — includes other financing costs of $0.8 and $0.7 respectively Interest Expense Allowance for funds used during construction — debt Public Utilities, Allowance For Funds Used During Construction, Capitalized Cost Of Debt The component of the allowance for funds used during construction during the period based on an assumed rate of return on debt capital used in financing the construction of regulated assets. Total interest charges and financing costs Interest and Debt Expense Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income taxes Income Tax Expense (Benefit) Net income Retirement Benefits [Abstract] Components of Net Periodic Benefit Cost (Credit) Schedule of Net Benefit Costs [Table Text Block] Benefit Plans and Other Postretirement Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Derivative Instrument Risk [Axis] Derivative Contract Type [Domain] Commodity Contract Commodity Contract [Member] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward] Balance at beginning of period Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs Purchases Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Purchases Settlements Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Settlements Net gains recognized as regulatory assets and liabilities Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Net Losses Gains Recognized As Regulatory Assets And Liabilities This element represents total gains (losses) for the period (realized and unrealized), arising from net assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), which are recognized in regulatory assets and liabilities. Balance at end of period Transfers into Level 3 Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers into Level 3 Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3 Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3 Environmental Contingencies [Abstract] -- None. No documentation exists for this element. -- Site Contingency [Table] Site Contingency [Table] Site Contingency [Line Items] Site Contingency [Line Items] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Total Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Income Tax Expense (Benefit) Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Accumulated other comprehensive loss at beginning of period Accumulated other comprehensive loss at end of period Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Total revenues Operating Segments [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Regulated Electric [Member] Regulated Electric [Member] The core operations of the regulated electric utility segment consists of the generation, transmission, and distribution of electricity. In addition, this segment includes sales for resale and provides wholesale transmission service to other entities. Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Total revenue from contracts with customers Product [Member] Retail Retail Distribution [Member] Retail Distribution [Member] Wholesale Wholesale Distribution [Member] Wholesale Distribution [Member] Transmission Transmission Services [Member] Transmission Services [Member] Other Other Services [Member] Other Services [Member] Alternative and Other [Member] Alternative and Other [Member] Alternative and Other [Member] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Residential Residential Customers [Member] Residential Customers [Member] Commercial and industrial (C&I) Commercial and Industrial Customers [Member] Commercial and Industrial Customers [Member] Other Other Customers [Member] Other Customers [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Total revenue from contracts with customers Revenue from Contract with Customer, Including Assessed Tax Line of Credit Facility [Abstract] Line of Credit Facility [Abstract] Letter of Credit Letter of Credit [Member] Term of letters of credit (in years) Line of Credit Facility, Expiration Period Interest charges and financing costs Other financing costs Debt Related Commitment Fees and Debt Issuance Costs Fair Value of Financial Assets and Liabilities Fair Value Disclosures [Text Block] Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block] Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block] Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block] Reconciliation of Unrecognized Tax Benefits Summary of Income Tax Contingencies [Table Text Block] Tax Benefits Associated with NOL and Tax Credit Carryforwards Tax Benefits Associated with Net Operating Loss (NOL) and Tax Credit Carryforwards [Table Text Block] Tabular disclosure of the tax benefits associated with net operating loss (NOL) and tax credit carryforwards. Interest Payable related to Unrecognized Tax Benefits [Table Text Block] Interest Payable related to Unrecognized Tax Benefits [Table Text Block] Interest Payable related to Unrecognized Tax Benefits Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instruments, Gain (Loss) [Table] Other Derivative Instruments Not Designated as Hedging Instrument [Member] Electric Commodity Electric Commodity Contract [Member] Derivative instrument whose primary underlying risk is tied to electric commodity prices. Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract] Impact of Derivative Activity on Accumulated Other Comprehensive Loss Regulatory Assets and Liabilities and Income [Abstract] -- None. No documentation exists for this element. -- Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities Derivative Instruments Gain Loss Reclassified To Regulatory Assets And Liabilities Net Derivative Instruments Gain Loss Reclassified To Regulatory Assets And Liabilities Net Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract] Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract] -- None. No documentation exists for this element. -- Derivative instruments designated as fair value hedges Fair Value Hedges, Net Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Variable Interest Entities by Classification of Entity [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Independent Power Producing Entities Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member] Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Purchased Power Agreements [Abstract] Purchased Power Agreements [Abstract] -- None. No documentation exists for this element. -- Generating capacity (in MW) Generating capacity under long term purchased power agreements Generating capacity under long-term purchased power agreements. Purchase Power Agreement Expiration (year) Purchase Power Agreement Expiration The expiration of purchase power agreements currently under contract (year). Income Taxes Income Tax Disclosure [Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Statement of Cash Flows [Abstract] Operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Amortization and Accretion, Net Demand side management program amortization Amortization of Regulatory Asset Deferred income taxes Deferred Income Tax Expense (Benefit) Allowance for equity funds used during construction Other, net Other Operating Activities, Cash Flow Statement Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable Increase (Decrease) in Accounts and Other Receivables Accrued unbilled revenues Increase (Decrease) in Unbilled Receivables Inventories Increase (Decrease) in Inventories Prepayments and other Increase (Decrease) in Other Current Assets Accounts payable Increase (Decrease) in Accounts Payable Net regulatory assets and liabilities Increase (Decrease) in Regulatory Assets and Liabilities Other current liabilities Increase (Decrease) in Other Current Liabilities Pension and other employee benefit obligations Increase (Decrease) in Employee Related Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Investing activities Net Cash Provided by (Used in) Investing Activities [Abstract] Utility capital/construction expenditures Payments to Acquire Productive Assets Allowance for equity funds used during construction Allowance for Funds Used During Construction, Investing Activities Investments in utility money pool arrangement Investments In Utility Money Pool Arrangement Investments made during the reporting period into the utility money pool borrowing arrangement among approved affiliates. Repayments from utility money pool arrangement Repayments From Utility Money Pool Arrangement Repayments received during the reporting period of amounts previously invested into the utility money pool borrowing arrangement among approved affiliates. Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Financing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from short-term borrowings, net Proceeds from (Repayments of) Short-term Debt Borrowings under utility money pool arrangement Borrowings Under Utility Money Pool Arrangement Borrowings made during the reporting period from the utility money pool borrowing arrangement among approved affiliates. Repayments under utility money pool arrangement Repayments Under Utility Money Pool Arrangement Repayments of amounts during the reporting period previously borrowed from the utility money pool borrowing arrangement among approved affiliates. Capital contributions from parent Proceeds from Contributions from Parent Repayment of long-term debt Repayments of Long-term Debt Dividends paid to parent Payments of Ordinary Dividends, Common Stock Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net change in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Cash paid for interest (net of amounts capitalized) Interest Paid, Excluding Capitalized Interest, Operating Activities Cash paid for income taxes, net Income Taxes Paid, Net Supplemental disclosure of non-cash investing and financing transactions: Other Noncash Investing and Financing Items [Abstract] Property, plant and equipment additions in accounts payable Capital Expenditures Incurred but Not yet Paid Inventory transfers to plant, property and equipment Inventory transfers to plant, property and equipment Amount of increase (decrease) of plant, property and equipment reclassified from inventory. Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Schedule of Operating Lease Right-of-Use Assets Assets and Liabilities, Lessee [Table Text Block] Assets and Liabilities, Lessee [Table Text Block] Schedule of Components of Lease Expense Lease, Cost [Table Text Block] Schedule of Future Commitments under Operating Leases Lessee, Operating Lease, Liability, Maturity [Table Text Block] Operating Leases after Adoption of ASC Topic 842 Operating Lease Liabilities, Payments Due [Abstract] 2019 Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2020 Lessee, Operating Lease, Liability, Payments, Due Year Two 2021 Lessee, Operating Lease, Liability, Payments, Due Year Three 2022 Lessee, Operating Lease, Liability, Payments, Due Year Four 2023 Lessee, Operating Lease, Liability, Payments, Due Year Five Thereafter Lessee, Operating Lease, Liability, Payments, Due after Year Five Total minimum obligation Lessee, Operating Lease, Liability, Payments, Due Interest component of obligation Lessee, Operating Lease, Liability, Undiscounted Excess Amount Present value of minimum obligation Less current portion Operating Lease, Liability, Current Noncurrent operating lease liabilities Weighted-average discount rate Operating Lease, Weighted Average Discount Rate, Percent Weighted-average remaining lease term in years Operating Lease, Weighted Average Remaining Lease Term Operating Leases before Adoption of ASC 842 Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2019 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2020 Operating Leases, Future Minimum Payments, Due in Two Years 2021 Operating Leases, Future Minimum Payments, Due in Three Years 2022 Operating Leases, Future Minimum Payments, Due in Four Years 2023 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Pension Plan [Member] Pension Plan [Member] Other Postretirement Benefits Plan [Member] Other Postretirement Benefits Plan [Member] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Xcel Energy Inc. Parent Company [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Components of Net Periodic Benefit Cost (Credit) [Abstract] Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Amortization of prior service cost (credit) Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Amortization of net loss (gain) Defined Benefit Plan, Amortization of Gain (Loss) Net periodic benefit cost (credit) Defined Benefit Plan Net Benefit Cost (Credit) Recognized Before Regulatory Adjustments The total mount of net periodic benefit cost, before regulatory adjustments, for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain or loss, prior service cost or credit, transition asset or obligation, and gain or loss due to settlements or curtailments, before regulatory adjustments. Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation The additional amount of credits not recognized in net periodic benefit as reported in the financial statements of the entity due to effects of regulation. Net benefit cost (credit) recognized for financial reporting Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Total contributions to the pension plans during the period Payment for Pension Benefits Number of Xcel Energy's pension plans to which contributions were made Defined benefit plan number of pension plans to which contributions were made Number of pension plans to which contributions were made during the period. Liabilities and Equity Capitalization, Long-term Debt and Equity [Abstract] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, shares outstanding (in shares) Accounts Receivable, Net Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Inventories Schedule of Utility Inventory [Table Text Block] Property, Plant and Equipment, Net Public Utility Property, Plant, and Equipment [Table Text Block] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Portion at Fair Value Measurement [Member] Estimate of Fair Value Measurement [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value Measured on a Recurring Basis Fair Value, Measurements, Recurring [Member] Fair Value, Measurements, Nonrecurring Fair Value, Measurements, Nonrecurring [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other Current Assets Other Current Assets [Member] Other Noncurrent Assets [Member] Other Noncurrent Assets [Member] Other Current Liabilities Other Current Liabilities [Member] Other Noncurrent Liabilities [Member] Other Noncurrent Liabilities [Member] Commodity Contract [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Derivative Asset, Collateral, Obligation to Return Cash, Offset Derivative Asset, Collateral, Obligation to Return Cash, Offset Derivative Liability, Collateral, Right to Reclaim Cash, Offset Derivative Liability, Collateral, Right to Reclaim Cash, Offset Derivative Asset, Fair Value, Gross Asset Derivative Asset, Fair Value, Gross Asset Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset Derivative Liability, Fair Value, Gross Liability Derivative Liability, Fair Value, Gross Liability