3.19.1 html 170 240 1 true 59 0 false 8 false false R1.htm 0001000 - Document - Document and Entity Information Sheet http://www.xcelenergy.com/role/DocumentAndEntityInformation Document and Entity Information Cover 1 false false R2.htm 1001000 - Statement - CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY (UNAUDITED) Sheet http://www.xcelenergy.com/role/ConsolidatedStatementsOfCommonStockholdersEquityUnaudited CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY (UNAUDITED) Statements 2 false false R3.htm 1001000 - Statement - STATEMENTS OF INCOME (UNAUDITED) Sheet http://www.xcelenergy.com/role/StatementsOfIncomeUnaudited STATEMENTS OF INCOME (UNAUDITED) Statements 3 false false R4.htm 1001501 - Statement - STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) Sheet http://www.xcelenergy.com/role/StatementsOfIncomeUnauditedParenthetical STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) Statements 4 false false R5.htm 1002000 - Statement - STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) Sheet http://www.xcelenergy.com/role/StatementsOfComprehensiveIncomeUnaudited STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) Statements 5 false false R6.htm 1002501 - Statement - STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) Sheet http://www.xcelenergy.com/role/StatementsOfComprehensiveIncomeUnauditedParenthetical STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) Statements 6 false false R7.htm 1003000 - Statement - STATEMENTS OF CASH FLOWS (UNAUDITED) Sheet http://www.xcelenergy.com/role/StatementsOfCashFlowsUnaudited STATEMENTS OF CASH FLOWS (UNAUDITED) Statements 7 false false R8.htm 1004000 - Statement - BALANCE SHEETS (UNAUDITED) Sheet http://www.xcelenergy.com/role/BalanceSheetsUnaudited BALANCE SHEETS (UNAUDITED) Statements 8 false false R9.htm 1004501 - Statement - BALANCE SHEETS (UNAUDITED) (Parenthetical) Sheet http://www.xcelenergy.com/role/BalanceSheetsUnauditedParenthetical BALANCE SHEETS (UNAUDITED) (Parenthetical) Statements 9 false false R10.htm 2101100 - Disclosure - Management's Opinion Sheet http://www.xcelenergy.com/role/ManagementsOpinion Management's Opinion Notes 10 false false R11.htm 2102100 - Disclosure - Summary of Significant Accounting Policies Sheet http://www.xcelenergy.com/role/SummaryOfSignificantAccountingPolicies Summary of Significant Accounting Policies Notes 11 false false R12.htm 2103100 - Disclosure - Accounting Pronouncements Sheet http://www.xcelenergy.com/role/AccountingPronouncements Accounting Pronouncements Notes 12 false false R13.htm 2104100 - Disclosure - Selected Balance Sheet Data Sheet http://www.xcelenergy.com/role/SelectedBalanceSheetData Selected Balance Sheet Data Notes 13 false false R14.htm 2105100 - Disclosure - Borrowings and Other Financing Instruments Sheet http://www.xcelenergy.com/role/BorrowingsAndOtherFinancingInstruments Borrowings and Other Financing Instruments Notes 14 false false R15.htm 2106100 - Disclosure - Revenues Sheet http://www.xcelenergy.com/role/Revenues Revenues Notes 15 false false R16.htm 2107100 - Disclosure - Income Taxes Sheet http://www.xcelenergy.com/role/IncomeTaxes Income Taxes Notes 16 false false R17.htm 2108100 - Disclosure - Fair Value of Financial Assets and Liabilities Sheet http://www.xcelenergy.com/role/FairValueOfFinancialAssetsAndLiabilities Fair Value of Financial Assets and Liabilities Notes 17 false false R18.htm 2109100 - Disclosure - Benefit Plans and Other Postretirement Benefits Sheet http://www.xcelenergy.com/role/BenefitPlansAndOtherPostretirementBenefits Benefit Plans and Other Postretirement Benefits Notes 18 false false R19.htm 2110100 - Disclosure - Commitments and Contingencies Sheet http://www.xcelenergy.com/role/CommitmentsAndContingencies Commitments and Contingencies Notes 19 false false R20.htm 2304301 - Disclosure - Selected Balance Sheet Data (Tables) Sheet http://www.xcelenergy.com/role/SelectedBalanceSheetDataTables Selected Balance Sheet Data (Tables) Tables http://www.xcelenergy.com/role/SelectedBalanceSheetData 20 false false R21.htm 2305301 - Disclosure - Borrowings and Other Financing Instruments (Tables) Sheet http://www.xcelenergy.com/role/BorrowingsAndOtherFinancingInstrumentsTables Borrowings and Other Financing Instruments (Tables) Tables http://www.xcelenergy.com/role/BorrowingsAndOtherFinancingInstruments 21 false false R22.htm 2306301 - Disclosure - Revenues (Tables) Sheet http://www.xcelenergy.com/role/RevenuesTables Revenues (Tables) Tables http://www.xcelenergy.com/role/Revenues 22 false false R23.htm 2307301 - Disclosure - Income Taxes (Tables) Sheet http://www.xcelenergy.com/role/IncomeTaxesTables Income Taxes (Tables) Tables http://www.xcelenergy.com/role/IncomeTaxes 23 false false R24.htm 2308301 - Disclosure - Fair Value of Financial Assets and Liabilities (Tables) Sheet http://www.xcelenergy.com/role/FairValueOfFinancialAssetsAndLiabilitiesTables Fair Value of Financial Assets and Liabilities (Tables) Tables http://www.xcelenergy.com/role/FairValueOfFinancialAssetsAndLiabilities 24 false false R25.htm 2309301 - Disclosure - Benefit Plans and Other Postretirement Benefits (Tables) Sheet http://www.xcelenergy.com/role/BenefitPlansAndOtherPostretirementBenefitsTables Benefit Plans and Other Postretirement Benefits (Tables) Tables http://www.xcelenergy.com/role/BenefitPlansAndOtherPostretirementBenefits 25 false false R26.htm 2310301 - Disclosure - Commitments and Contingencies Commitments and Contingencies (Tables) Sheet http://www.xcelenergy.com/role/CommitmentsAndContingenciesCommitmentsAndContingenciesTables Commitments and Contingencies Commitments and Contingencies (Tables) Tables 26 false false R27.htm 2402401 - Disclosure - Summary of Significant Accounting Policies accounting policies (Details) Sheet http://www.xcelenergy.com/role/SummaryOfSignificantAccountingPoliciesAccountingPoliciesDetails Summary of Significant Accounting Policies accounting policies (Details) Details 27 false false R28.htm 2403401 - Disclosure - Accounting Pronouncements (Details) Sheet http://www.xcelenergy.com/role/AccountingPronouncementsDetails Accounting Pronouncements (Details) Details http://www.xcelenergy.com/role/AccountingPronouncements 28 false false R29.htm 2404402 - Disclosure - Selected Balance Sheet Data (Details) Sheet http://www.xcelenergy.com/role/SelectedBalanceSheetDataDetails Selected Balance Sheet Data (Details) Details http://www.xcelenergy.com/role/SelectedBalanceSheetDataTables 29 false false R30.htm 2404403 - Disclosure - Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) Sheet http://www.xcelenergy.com/role/SelectedBalanceSheetDataBalanceSheetRelatedDisclosuresPropertyPlantAndEquipmentDetails Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) Details 30 false false R31.htm 2404404 - Disclosure - Selected Balance Sheet Data Inventory (Details) Sheet http://www.xcelenergy.com/role/SelectedBalanceSheetDataInventoryDetails Selected Balance Sheet Data Inventory (Details) Details 31 false false R32.htm 2405402 - Disclosure - Borrowings and Other Financing Instruments, Short-Term Borrowings (Details) Sheet http://www.xcelenergy.com/role/BorrowingsAndOtherFinancingInstrumentsShortTermBorrowingsDetails Borrowings and Other Financing Instruments, Short-Term Borrowings (Details) Details 32 false false R33.htm 2405403 - Disclosure - Borrowings and Other Financing Instruments, Letters of Credit (Details) Sheet http://www.xcelenergy.com/role/BorrowingsAndOtherFinancingInstrumentsLettersOfCreditDetails Borrowings and Other Financing Instruments, Letters of Credit (Details) Details 33 false false R34.htm 2405404 - Disclosure - Borrowings and Other Financing Instruments, Credit Facility (Details) Sheet http://www.xcelenergy.com/role/BorrowingsAndOtherFinancingInstrumentsCreditFacilityDetails Borrowings and Other Financing Instruments, Credit Facility (Details) Details 34 false false R35.htm 2406402 - Disclosure - Revenues (Details) Sheet http://www.xcelenergy.com/role/RevenuesDetails Revenues (Details) Details http://www.xcelenergy.com/role/RevenuesTables 35 false false R36.htm 2407402 - Disclosure - Income Taxes (Details) Sheet http://www.xcelenergy.com/role/IncomeTaxesDetails Income Taxes (Details) Details http://www.xcelenergy.com/role/IncomeTaxesTables 36 false false R37.htm 2408402 - Disclosure - Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) Sheet http://www.xcelenergy.com/role/FairValueOfFinancialAssetsAndLiabilitiesDerivativeInstrumentsDetails Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) Details 37 false false R38.htm 2408403 - Disclosure - Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) Sheet http://www.xcelenergy.com/role/FairValueOfFinancialAssetsAndLiabilitiesImpactOfDerivativeActivityDetails Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) Details 38 false false R39.htm 2408404 - Disclosure - Fair Value of Financial Assets and Liabilities, Fair Value Measurements (Details) Sheet http://www.xcelenergy.com/role/FairValueOfFinancialAssetsAndLiabilitiesFairValueMeasurementsDetails Fair Value of Financial Assets and Liabilities, Fair Value Measurements (Details) Details 39 false false R40.htm 2408405 - Disclosure - Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) Sheet http://www.xcelenergy.com/role/FairValueOfFinancialAssetsAndLiabilitiesFairValueOfFinancialAssetsAndLiabilitiesChangesInLevel3CommodityDerivativesDetails Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) Details 40 false false R41.htm 2408406 - Disclosure - Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) Sheet http://www.xcelenergy.com/role/FairValueOfFinancialAssetsAndLiabilitiesFairValueOfLongTermDebtDetails Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) Details 41 false false R42.htm 2409402 - Disclosure - Benefit Plans and Other Postretirement Benefits (Details) Sheet http://www.xcelenergy.com/role/BenefitPlansAndOtherPostretirementBenefitsDetails Benefit Plans and Other Postretirement Benefits (Details) Details http://www.xcelenergy.com/role/BenefitPlansAndOtherPostretirementBenefitsTables 42 false false R43.htm 2410402 - Disclosure - Commitments and Contingencies, Purchased Power Agreements (Details) Sheet http://www.xcelenergy.com/role/CommitmentsAndContingenciesPurchasedPowerAgreementsDetails Commitments and Contingencies, Purchased Power Agreements (Details) Details 43 false false R44.htm 2410403 - Disclosure - Commitments and Contingencies Commitments and Contingencies, Environmental Contingencies - Site Contingencies (Details) Sheet http://www.xcelenergy.com/role/CommitmentsAndContingenciesCommitmentsAndContingenciesEnvironmentalContingenciesSiteContingenciesDetails Commitments and Contingencies Commitments and Contingencies, Environmental Contingencies - Site Contingencies (Details) Details 44 false false R45.htm 2410405 - Disclosure - Commitments and Contingencies, Rate Matters, SPS (Details) Sheet http://www.xcelenergy.com/role/CommitmentsAndContingenciesRateMattersSpsDetails Commitments and Contingencies, Rate Matters, SPS (Details) Details 45 false false R46.htm 2410406 - Disclosure - Commitments and Contingencies Commitments and Contingencies, Leases - Right-of-Use Assets (Details) Sheet http://www.xcelenergy.com/role/CommitmentsAndContingenciesCommitmentsAndContingenciesLeasesRightOfUseAssetsDetails Commitments and Contingencies Commitments and Contingencies, Leases - Right-of-Use Assets (Details) Details 46 false false R47.htm 2410407 - Disclosure - Commitments and Contingencies Commitments and Contingencies, Leases - Components of Lease Expense (Details) Sheet http://www.xcelenergy.com/role/CommitmentsAndContingenciesCommitmentsAndContingenciesLeasesComponentsOfLeaseExpenseDetails Commitments and Contingencies Commitments and Contingencies, Leases - Components of Lease Expense (Details) Details 47 false false R48.htm 2410408 - Disclosure - Commitments and Contingencies Commitments and Contingencies, Leases - Future Commitments (Details) Sheet http://www.xcelenergy.com/role/CommitmentsAndContingenciesCommitmentsAndContingenciesLeasesFutureCommitmentsDetails Commitments and Contingencies Commitments and Contingencies, Leases - Future Commitments (Details) Details 48 false false R49.htm 2413402 - Disclosure - Other Comprehensive Income (Details) Sheet http://www.xcelenergy.com/role/OtherComprehensiveIncomeDetails Other Comprehensive Income (Details) Details 49 false false All Reports Book All Reports sps-20190331.xml sps-20190331.xsd sps-20190331_cal.xml sps-20190331_def.xml sps-20190331_lab.xml sps-20190331_pre.xml http://xbrl.sec.gov/stpr/2018-01-31 http://fasb.org/srt/2018-01-31 http://fasb.org/us-gaap/2018-01-31 http://xbrl.sec.gov/invest/2013-01-31 http://xbrl.sec.gov/dei/2018-01-31 true true