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Regulatory and Rate Matters - PNM (Details) |  |  |  |  |  |  |  | 3 Months Ended | 6 Months Ended | 12 Months Ended | 40 Months Ended |  |  |  |  |  |  |
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Aug. 05, 2016 | Aug. 04, 2016 USD ($) | Apr. 15, 2016 USD ($) GWh | Jan. 21, 2016 MW | Jan. 15, 2016 LeaseAgreements | Aug. 27, 2015 USD ($) | Mar. 20, 2015 USD ($) party | Jun. 30, 2016 USD ($) | Jun. 30, 2015 USD ($) MW | Jun. 30, 2016 USD ($) | Jun. 30, 2015 USD ($) MW | Dec. 31, 2015 | Jun. 30, 2016 USD ($) | Jul. 08, 2016 MW | Apr. 26, 2016 USD ($) turbine MW | Feb. 26, 2016 USD ($) | Jan. 31, 2016 MW | Dec. 31, 2013 | Mar. 01, 2013 | Dec. 31, 2012 USD ($)
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net book value |  |  |  |  |  |  |  | $ 272,200,000 |  | $ 272,200,000 |  |  | $ 272,200,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Clean Air Act, Balanced Draft Technology [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net book value |  |  |  |  |  |  |  | 51,300,000 |  | 51,300,000 |  |  | 51,300,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] | San Juan Generating Station Units 2 and 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Newly identified replacement gas-fired generation (in megawatts) | MW |  |  |  |  |  |  |  |  | 187 |  | 187 |  |  |  | 80 |  |  |  |  |
Number of aeroderivative units (in turbines) | turbine |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |
Replacement gas-fired aeroderivative generation (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 40 |  |  |  |  |
Cost of replacement gas-fired unit |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 86,800,000 |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station, Unit 2 Leases [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts purchased (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 64.1 |  |  |
Number of leases under which assets were purchased | LeaseAgreements |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated annual property tax expense |  |  |  |  |  |  |  | 800,000 |  | 800,000 |  |  | 800,000 |  |  |  |  |  |  |
Number of leases under which lease term was extended | LeaseAgreements |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lease term extension period |  |  |  |  | 8 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net book value |  |  |  |  |  |  |  | 161,300,000 |  | 161,300,000 |  |  | 161,300,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station, Unit 1 Leases, extended [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated annual property tax expense |  |  |  |  |  |  |  | 1,500,000 |  | 1,500,000 |  |  | 1,500,000 |  |  |  |  |  |  |
Estimated annual rent expense |  |  |  |  |  |  |  | 18,100,000 |  | 18,100,000 |  |  | 18,100,000 |  |  |  |  |  |  |
Number of leases under which lease term was extended | LeaseAgreements |  |  |  |  | 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lease term extension period |  |  |  |  | 8 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station, Units 1 and 2 Leases [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated annual property tax expense |  |  |  |  |  |  |  | 2,300,000 |  | 2,300,000 |  |  | 2,300,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Clean Air Act, Balanced Draft Technology [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Installation costs |  |  |  |  |  |  |  |  |  |  |  |  | 52,300,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Clean Air Act, SNCR [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Installation costs |  |  |  |  |  |  |  |  |  |  |  |  | 76,800,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease) |  |  |  |  |  | $ 123,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease) of non-fuel revenue |  |  |  |  |  | $ 121,700,000 |  |  |  | 121,500,000 |  |  |  |  |  |  |  |  |  |
Requested return on equity |  |  |  |  |  | 10.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease) for fuel related costs |  |  |  |  |  |  |  |  |  | (42,900,000) |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease) for non-fuel related revenues |  |  |  |  |  |  |  |  |  | (200,000) |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] | Clean Air Act, Balanced Draft Technology [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested base rate increase (decrease) |  |  |  |  |  | $ 40,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hearing examiner's recommended rate increase (decrease) of non-fuel revenue |  | $ 41,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hearing examiner's recommended return on equity |  | 9.575% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] | Palo Verde Nuclear Generating Station, Unit 2 Leases [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hearing examiner's proposed disallowance of recovery |  | $ 163,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] | Palo Verde Nuclear Generating Station, Unit 1 Leases, extended [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future minimum payments due |  |  |  |  |  |  |  | 120,300,000 |  | 120,300,000 |  |  | 120,300,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] | Palo Verde Nuclear Generating Station, Unit 1 Leases, extended [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hearing examiner's recommended rent expense recovery amount |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hearing examiner's recommended recovery amount on conversions |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] | Palo Verde Nuclear Generating Station, Units 1 and 2 Leases [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hearing examiner's recommended property tax recovery amount |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] | Alvarado square [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets |  |  |  |  |  |  |  | $ 4,000,000 |  | $ 4,000,000 |  |  | $ 4,000,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] | Alvarado square [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hearing examiner's recommended amount to not be recovered from retail customers |  | $ 4,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member] | Refined Coal [Member] | Subsequent Event [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hearing examiner's recommended percentage of revenue to be credited to customers |  | 100.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reasonable cost threshold |  |  |  |  |  |  |  | 3.00% |  | 3.00% |  |  | 3.00% |  |  |  |  | 3.00% |  |
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Wind Energy [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of diversification |  |  |  |  |  |  |  | 30.00% |  | 30.00% |  |  | 30.00% |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Solar Energy [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of diversification |  |  |  |  |  |  |  | 20.00% |  | 20.00% |  |  | 20.00% |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Distributed Generation [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of diversification |  |  |  |  |  |  |  | 3.00% |  | 3.00% |  |  | 3.00% |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Renewable Technologies [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of diversification |  |  |  |  |  |  |  | 5.00% |  | 5.00% |  |  | 5.00% |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Required Percentage by 2011 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of renewable energy in portfolio to electric sales |  |  |  |  |  |  |  | 10.00% |  | 10.00% |  |  | 10.00% |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Required Percentage by 2015 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of renewable energy in portfolio to electric sales |  |  |  |  |  |  |  | 15.00% |  | 15.00% |  |  | 15.00% |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Required Percentage by 2020 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required percentage of renewable energy in portfolio to electric sales |  |  |  |  |  |  |  | 20.00% |  | 20.00% |  |  | 20.00% |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Renewable Energy Rider [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved return on equity |  |  |  |  |  |  |  |  |  | 10.50% |  | 10.50% |  |  |  |  |  |  |  |
Proposal to collect funds under renewable energy procurement plan |  |  |  |  |  |  |  | $ 42,400,000 |  | $ 42,400,000 |  |  | $ 42,400,000 |  |  |  |  |  |  |
Annual revenue to be collected under rider rate |  |  |  |  |  |  |  | 50,000,000 |  | $ 50,000,000 |  |  | $ 50,000,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | 2017 Energy Efficiency and Load Management Program [Member] | Disincentives / Incentives Adder [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Program portfolio's total budget |  |  | $ 28,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Incentive based on target savings |  |  | $ 2,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Targeted savings (in gigawatt hours) | GWh |  |  | 75 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Integrated Resource Plan, 2011 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Frequency of IRP filings |  |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |
Planning period covered of IRP |  |  |  |  |  |  |  |  |  | 20 years |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Advanced Metering Infrastructure Costs [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated costs to be recovered |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 87,200,000 |  |  |  |
Estimated future investment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 33,000,000 |  |  |  |
Public Service Company of New Mexico [Member] | Advanced Metering Infrastructure Costs [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of time to either request a new hearing or withdraw application with regulatory body | 60 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Formula Transmission Rate Case [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of regulatory costs not yet approved |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,200,000
Return on equity |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  | 10.81%
Percentage ownership of EIP transmission line |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 60.00% |
Number of other parties entered into settlement agreement | party |  |  |  |  |  |  | 5 |  |  |  |  |  |  |  |  |  |  |  |  |
Approved rate increase (decrease) |  |  |  |  |  |  | $ 1,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Firm Requirements Wholesale Power Rate Case, Navopache [Member] [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts served under a short-term coordination tariff | MW |  |  |  | 10 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue for power sold under PSA |  |  |  |  |  |  |  | $ 4,700,000 | $ 6,400,000 | $ 10,000,000 | $ 13,400,000 |  |  |  |  |  |  |  |  |
PNMR Development [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Solar generation capacity (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 |  |  |  |  |  |

X
- Definition Estimated annual property tax expense + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Estimated annual rent expense + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Installation Capital Costs + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Lease term extension period + References No definition available. + Details
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