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Pension and Other Postretirement Benefits Pre-Tax Information about Prior Service Cost and Net Actuarial (Gain) loss in AOCI (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit) - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	$ (2,665)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	139,256us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Prior service cost (credit) - Experience loss (gain)	0us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostCreditArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Experience loss (gain)	34,345us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Prior service cost (credit) - Regulatory asset (liability) adjustment	0pnm_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansPriorServiceCostsRegulatoryAssetLiabilityAdjustmentBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Regulatory asset (liability) adjustment	(19,920)pnm_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetActuarialGainLossRegulatoryAssetLiabilityAdjustmentBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Prior service cost (credit) - Amortization recognized in net periodic benefit cost (income)	405us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Amortization recognized in net periodic benefit cost (income)	(5,469)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Prior service cost (credit) - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	(2,260)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	148,212us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Prior service cost (credit) - Amortization expected to be recognized in in 2015	(405)us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Amortization expected to be recognized in in 2015	6,224us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss - Experience loss (gain)	2,800us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	1,833us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Experience loss (gain)	2,040us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Regulatory asset (liability) adjustment	(1,183)pnm_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetActuarialGainLossRegulatoryAssetLiabilityAdjustmentBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Amortization recognized in net periodic benefit cost (income)	(88)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	2,602us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Net actuarial (gain) loss - Amortization expected to be recognized in in 2015	136us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_PublicServiceCompanyOfNewMexicoMember
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	0us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Experience loss (gain)	4,420us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Regulatory asset (liability) adjustment	(4,420)pnm_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetActuarialGainLossRegulatoryAssetLiabilityAdjustmentBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Amortization recognized in net periodic benefit cost (income)	0us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	0us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Amortization expected to be recognized in in 2015	0us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss - Experience loss (gain)	1,300us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at beginning of year	0us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Experience loss (gain)	(110)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Regulatory asset (liability) adjustment	110pnm_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetActuarialGainLossRegulatoryAssetLiabilityAdjustmentBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Amortization recognized in net periodic benefit cost (income)	0us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Amounts in AOCI not yet recognized in net periodic benefit cost (income) at end of year	0us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember
Net actuarial (gain) loss - Amortization expected to be recognized in in 2015	$ 0us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPensionPlansDefinedBenefitMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember

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Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Actuarial (Gain) Loss, Regulatory Asset (Liability) Adjustment, before Tax

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The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan.

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Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost.

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Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

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Amount included in accumulated other comprehensive income (AOCI) related to prior service cost (credit) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

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Amount before tax of cost (credit) of benefit changes attributable to plan participants' prior service resulting from a plan amendment or plan initiation that has not been recognized in net periodic benefit cost (credit).

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Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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Amount before tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit.

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