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It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. 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Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. 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Current assets are expected to be realized or consumed within one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 8 -Article 5 false 13 Total current assets 2 us-gaap_AssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 545584000 545584 false false false 2 false true false false 578205000 578205 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold, or consumed within one year (or the normal operating cycle, if longer). Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 9 -Article 5 true 14 Other Property and Investments: 1 pnm_OtherPropertyAndInvestmentsAbstract pnm false na duration Other Property And Investments [Abstract] false false false false false true false false false false false terselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string Other Property And Investments [Abstract] false 15 Investment in PVNGS lessor notes 2 pnm_InvestmentInPvngsLessorNotes pnm false debit instant Investment in PVNGS lessor notes false false false false false false false false false false false label false 1 false true false false 104212000 104212 false false false 2 false true false false 137511000 137511 false false false xbrli:monetaryItemType monetary Investment in PVNGS lessor notes No authoritative reference available. false 16 Equity investment in Optim Energy 2 us-gaap_EquityMethodInvestments us-gaap true debit instant No definition available. false false false false false false false false false false false false 1 false true false false 199693000 199693 false false false 2 false true false false 195666000 195666 false false false xbrli:monetaryItemType monetary This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment losses recognized. No authoritative reference available. false 17 Investments held by NDT 2 us-gaap_AvailableForSaleSecuritiesNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false false 1 false true false false 146327000 146327 false false false 2 false true false false 137032000 137032 false false false xbrli:monetaryItemType monetary Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. 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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 12 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph f -Article 7 false 19 Non-utility property, net of accumulated depreciation of $2,152 and $3,779 2 us-gaap_PropertyPlantAndEquipmentOther us-gaap true debit instant No definition available. false false false false false false false false false false false label false 1 false true false false 7499000 7499 false false false 2 false true false false 7923000 7923 false false false xbrli:monetaryItemType monetary This element represents capitalized assets classified as property, plant and equipment not otherwise defined in the taxonomy. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 false 20 Total other property and investments 2 pnm_TotalOtherPropertyAndInvestments pnm false debit instant Total other property and investments false false false false false false false false false false false totallabel false 1 false true false false 478888000 478888 false false false 2 false true false false 503660000 503660 false false false xbrli:monetaryItemType monetary Total other property and investments No authoritative reference available. true 21 Utility Plant: 1 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false terselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 22 Plant in service and plant held for future use 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService us-gaap true debit instant No definition available. false false false false false false false false false false false false 1 false true false false 4778761000 4778761 false false false 2 false true false false 4693530000 4693530 false false false xbrli:monetaryItemType monetary Period end amount of total gross PPE No authoritative reference available. false 23 Less accumulated depreciation and amortization 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation us-gaap true credit instant No definition available. false false false false false false false false false false false false 1 false true false false 1621612000 1621612 false false false 2 false true false false 1611496000 1611496 false false false xbrli:monetaryItemType monetary Period end book value of accumulated depreciation on property, plant and equipment (PPE) that is owned by the regulated operations of the public utility. No authoritative reference available. false 24 Net plant in service and plant held for future use 2 pnm_PublicUtilitiesPropertyPlantAndEquipmentInServicesNet pnm false debit instant Public utilities property plant and equipment in services net false false false false false false false false false false false totallabel false 1 false true false false 3157149000 3157149 false false false 2 false true false false 3082034000 3082034 false false false xbrli:monetaryItemType monetary Public utilities property plant and equipment in services net No authoritative reference available. true 25 Construction work in progress 2 us-gaap_ConstructionInProgressGross us-gaap true debit instant No definition available. false false false false false false false false false false false false 1 false true false false 156061000 156061 false false false 2 false true false false 181078000 181078 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date of long-lived asset under construction that include construction costs to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service. 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No authoritative reference available. false 27 Net utility plant 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 3391283000 3391283 false false false 2 false true false false 3332449000 3332449 false false false xbrli:monetaryItemType monetary Period end amount of total net PPE No authoritative reference available. true 28 Deferred Charges and Other Assets: 1 us-gaap_OtherAssetsNoncurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 29 Regulatory assets 2 us-gaap_RegulatoryAssetsNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false terselabel false 1 false true false false 516563000 516563 false false false 2 false true false false 524136000 524136 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. 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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 4, 17 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 4 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FIN39-1 -Paragraph 10A, 10B false 33 Other deferred charges 2 pnm_OtherDeferredCostsNetIncludingDeferredFinanceCosts pnm false debit instant Other Deferred Costs Net Including Deferred Finance Costs false false false false false false false false false false false terselabel false 1 false true false false 92867000 92867 false false false 2 false true false false 71181000 71181 false false false xbrli:monetaryItemType monetary Other Deferred Costs Net Including Deferred Finance Costs No authoritative reference available. false 34 Total deferred charges and other assets 2 pnm_TotalDeferredChargesAndOtherAssets pnm false debit instant Total deferred charges and other assets false false false false false false false false false false false totallabel false 1 false true false false 965054000 965054 false false false 2 false true false false 945607000 945607 false false false xbrli:monetaryItemType monetary Total deferred charges and other assets No authoritative reference available. true 35 Total assets 2 us-gaap_Assets us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 5380809000 5380809 false false false 2 false true false false 5359921000 5359921 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. 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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Article 5 false 39 Accounts payable 2 us-gaap_AccountsPayableCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false false 1 false true false false 102052000 102052 false false false 2 false true false false 111432000 111432 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). 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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 false 46 Deferred Credits and Other Liabilities: 1 us-gaap_OtherLiabilitiesNoncurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 47 Accumulated deferred income taxes 2 us-gaap_DeferredTaxLiabilitiesNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false false 1 false true false false 550481000 550481 false false false 2 false true false false 531166000 531166 false false false xbrli:monetaryItemType monetary Represents the noncurrent portion of deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. A noncurrent taxable temporary difference is a difference between the tax basis and the carrying amount of a noncurrent asset or liability in the financial statements prepared in accordance with generally accepted accounting principles. In a classified statement of financial position, an enterprise shall separate deferred tax liabilities and assets into a current amount and a noncurrent amount. Deferred tax liabilities and assets shall be classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, shall be classified according to the expected reversal date of the temporary difference. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 41, 42 false 48 Accumulated deferred investment tax credits 2 us-gaap_AccumulatedDeferredInvestmentTaxCredit us-gaap true credit instant No definition available. false false false false false false false false false false false false 1 false true false false 18696000 18696 false false false 2 false true false false 20518000 20518 false false false xbrli:monetaryItemType monetary The noncurrent portion of the reserve for accumulated deferred investment tax credits as of the balance sheet date. This is the remaining investment credit, which will reduce the cost of services collected from ratepayers by a ratable portion over the investment's regulatory life. 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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 24 -Article 5 true 55 Total liabilities 2 us-gaap_Liabilities us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 3512849000 3512849 false false false 2 false true false false 3509316000 3509316 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future. 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