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Segment Information (Narrative and Major Customers) (Details) (Electric operating revenues [Member]) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
First Choice [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Operating revenues from continuing operations (as a percent) | 15.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_FirstChoiceMember | 17.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_FirstChoiceMember |
Unaffiliated Customer of Texas-New Mexico Power Company One [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Operating revenues from continuing operations (as a percent) | 15.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyOneMember | 16.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyOneMember | 17.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyOneMember
Unaffiliated Customer of Texas-New Mexico Power Company Two [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Operating revenues from continuing operations (as a percent) | 11.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyTwoMember | 10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyTwoMember | 10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / us-gaap_MajorCustomersAxis = pnm_UnaffiliatedCustomerOfTexasNewMexicoPowerCompanyTwoMember
PNMR and PNM [Member] | Maximum [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Number of Customers that make up 10 percent of total revenue | 0pnm_NumberofCustomersthatmakeup10percentoftotalrevenue / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |
Operating revenues from continuing operations (as a percent) | 10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / dei_LegalEntityAxis = pnm_PnmrAndPnmMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |
Texas-New Mexico Power Company [Member] | Maximum [Member] |  |  |
Concentration Risk [Line Items] |  |  |
Number of Customers that make up 10 percent of total revenue | 2pnm_NumberofCustomersthatmakeup10percentoftotalrevenue / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesMember / dei_LegalEntityAxis = pnm_TexasNewMexicoPowerCompanyMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |

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