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Commitments and Contingencies - The Clean Air Act (Details) |  |  |  |  |  |  | 1 Months Ended | 12 Months Ended | 35 Months Ended |  |  |  |  |
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Feb. 09, 2016 | Dec. 31, 2015 USD ($) | Dec. 16, 2015 USD ($) MWh MW | Oct. 23, 2015 | Jul. 17, 2015 | Dec. 20, 2013 USD ($) $ / kw MW | Aug. 31, 2011 generating_unit | Dec. 31, 2016 USD ($) lb / MMBTU generating_unit joint_owner MW | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Jan. 31, 2016 USD ($) | Jan. 26, 2016 state | Jul. 31, 2015 MW | Aug. 06, 2012 compliance_alternative | Jul. 31, 2005 T | Dec. 31, 1999 state
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant in service, held for future use, and to be abandoned |  | $ 6,307,261,000 |  |  |  |  |  | $ 6,944,534,000 | $ 6,307,261,000 |  |  |  |  |  |  |
Accumulated depreciation and amortization |  | 2,058,772,000 |  |  |  |  |  | 2,334,938,000 | 2,058,772,000 |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  | 15,011,000 | 167,471,000 | $ 1,062,000 |  |  |  |  |  |
Reversal of deferred items related to BART at SJGS |  |  |  |  |  |  |  | 0 | 1,826,000 | 0 |  |  |  |  |  |
Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved lease extension term |  |  |  |  | 25 years |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant in service, held for future use, and to be abandoned |  | 4,833,303,000 |  |  |  |  |  | 5,359,211,000 | 4,833,303,000 |  |  |  |  |  |  |
Accumulated depreciation and amortization |  | 1,569,549,000 |  |  |  |  |  | 1,809,528,000 | 1,569,549,000 |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  | 15,011,000 | 167,471,000 | 1,062,000 |  |  |  |  |  |
Reversal of deferred items related to BART at SJGS |  |  |  |  |  |  |  | $ 0 | 1,826,000 | $ 0 |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units (in generating units) | generating_unit |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |
Share of costs |  |  |  |  |  |  |  | 46.30% |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Surface [Member] | Loss on long-term purchase commitment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  | 16,500,000 |  |  |  |  |  |  | 16,500,000 |  |  |  |  |  |  |
Estimate of possible loss |  |  |  |  |  |  |  | $ 102,000,000 |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant in service, held for future use, and to be abandoned |  | 468,200,000 |  |  |  |  |  | 471,800,000 | 468,200,000 |  |  |  |  |  |  |
Accumulated depreciation and amortization |  | 193,300,000 |  |  |  |  |  | 203,900,000 | 193,300,000 |  |  |  |  |  |  |
Construction work in progress |  | 2,200,000 |  |  |  |  |  |  | 2,200,000 |  |  |  |  |  |  |
Net book value |  | $ 277,100,000 |  |  |  |  |  | $ 267,900,000 | 277,100,000 |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units (in generating units) | generating_unit |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Four Corners Units 4 and 5 (Coal) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share of costs |  |  |  |  |  |  |  | 13.00% |  |  |  |  |  |  |  |
Plant in service, held for future use, and to be abandoned |  |  |  |  |  |  |  | $ 188,026,000 |  |  |  |  |  |  |  |
Accumulated depreciation and amortization |  |  |  |  |  |  |  | 103,584,000 |  |  |  |  |  |  |  |
Construction work in progress |  |  |  |  |  |  |  | $ 52,869,000 |  |  |  |  |  |  |  |
PNMR and PNM [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts | MW |  |  |  |  |  |  |  | 134 |  |  |  |  |  |  |  |
PNMR Development [Member] | Energy Equipment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost of installing equipment |  |  |  |  |  |  |  | $ 7,600,000 |  |  |  |  |  |  |  |
Environmental Protection Agency [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units (in generating units) | generating_unit |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |  |
Environmental Protection Agency and NMED [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of time to comply after approval |  |  |  |  |  |  | 15 months |  |  |  |  |  |  |  |  |
Clean Air Act related to Regional Haze [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of states to address regional haze | state |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50
Potential to emit tons per year of visibility impairing pollution, maximum (in tons) | T |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 250 |
Clean Air Act, SCR [Member] [Member] | Public Service Company of New Mexico [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Minimum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated total capital cost if requirement occurred |  |  |  |  |  |  |  | 824,000,000 |  |  |  |  |  |  |  |
Clean Air Act, SCR [Member] [Member] | Public Service Company of New Mexico [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Maximum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated total capital cost if requirement occurred |  |  |  |  |  |  |  | $ 910,000,000 |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of other entities (in joint owner) | joint_owner |  |  |  |  |  |  |  | 8 |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | San Juan Generating Station Unit 4 [Member] | CALIFORNIA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of other entities (in joint owner) | joint_owner |  |  |  |  |  |  |  | 3 |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated costs to remain unrecovered |  |  | $ 20,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  |  | $ 21,600,000 |  |  |  |  |  |  |
Net expense |  |  |  |  |  |  |  | $ 3,700,000 |  |  |  |  |  |  |  |
Reclamation expense |  |  |  |  |  |  |  | $ 4,500,000 |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Overall reduction of ownership (in megawatts) | MW |  |  |  |  |  | 340 |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested time period to recover retired units NBV |  |  | 20 years |  |  | 20 years |  |  | 20 years |  |  |  |  |  |  |
Number of megawatts of gas-fired generation (in megawatts) | MW |  |  |  |  |  | 177 |  |  |  |  |  |  |  |  |  |
Newly identified replacement solar generation (in megawatts) | MW |  |  |  |  |  | 40 |  |  |  |  |  |  |  |  |  |
Current ownership (in megawatts) | MW |  |  | 418 |  |  |  |  |  |  |  |  |  |  |  |  |
Recovery percentage of estimated undepreciated value |  | 50.00% | 50.00% |  |  |  |  | 50.00% | 50.00% |  |  |  |  |  |  |
Estimated undepreciated value |  | $ 255,300,000 |  |  |  |  |  |  | $ 255,300,000 |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  |  | 127,600,000 |  |  |  |  |  |  |
Reversal of deferred items related to BART at SJGS |  |  |  |  |  |  |  |  | 1,800,000 |  |  |  |  |  |  |
Accumulated plant write-off, disallowance |  |  |  |  |  |  |  | $ 128,600,000 |  |  |  |  |  |  |  |
Net carrying value |  |  |  |  |  |  |  | $ 139,300,000 |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] | Increase in coal mine decommissioning liability [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  |  | 165,700,000 |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated undepreciated value |  |  | $ 151,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional ownership to be obtained (in megawatts) | MW |  |  | 65 |  |  |  |  |  |  |  |  |  | 132 |  |  |
Estimated rate base value |  |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Coal-fired generation (in megawatts) | MW |  |  | 197 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatt hours of renewable energy certificates to be acquired and retired (in megawatt hours) | MWh |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership held by exiting owners |  |  |  |  |  |  |  | 38.80% |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  | 38.50% |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership held by exiting owners |  |  |  |  |  |  |  | 50.00% |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  | 50.00% |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Maximum [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual cost of renewable energy credits, maximum |  |  | $ 7,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Portion of costs for SNCRs and BDT equipment |  |  |  |  |  |  |  |  |  |  | $ 77,900,000 |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Minimum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated installation capital costs |  |  |  |  |  |  |  | $ 85,000,000 |  |  |  |  |  |  |  |
Estimated portion of total capital costs if requirement occurred |  |  |  |  |  |  |  | 105,000,000 |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Maximum [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated installation capital costs |  |  |  |  |  |  |  | 90,000,000 |  |  |  |  |  |  |  |
Estimated portion of total capital costs if requirement occurred |  |  |  |  |  |  |  | 110,000,000 |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Maximum [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated installation capital costs |  |  |  |  |  | $ 82,000,000 |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Scenario, Plan [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  |  |  |  |  |  | 66.30% |  |  |
Clean Air Act, SNCR [Member] | Public Service Company of New Mexico [Member] | Scenario, Plan [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  |  |  |  |  |  | 77.30% |  |  |
Clean Air Act, SNCR [Member] | PNMR and PNM [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts | MW |  |  | 134 |  |  | 134 |  |  |  |  |  |  |  |  |  |
Proposed value per kilowatt (in dollars per kilowatt) | $ / kw |  |  |  |  |  | 2,500 |  |  |  |  |  |  |  |  |  |
Clean Air Act, SNCR [Member] | PNMR Development [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional ownership to be obtained (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  | 65 |  |  |
Reimbursement amount |  |  |  |  |  |  |  | $ 600,000 |  |  |  |  |  |  |  |
Potential acquisition of ownership (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  | 65 |  |  |
Restructuring fee |  |  |  |  |  |  |  |  | $ 3,100,000 |  |  |  |  |  |  |
Clean Air Act, SNCR Hearing Examiner Recommended Denial [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional ownership to be obtained (in megawatts) | MW |  |  | 132 |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act, Post-2022 Coal Supply future rate case [Member] | Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of time for stipulation agreement |  |  | 6 months |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act Related to Post Combustion Controls [Member] | Public Service Company of New Mexico [Member] | Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of compliance alternatives | compliance_alternative |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |
Government standard emissions limit (in pounds per MMBTU) | lb / MMBTU |  |  |  |  |  |  |  | 0.015 |  |  |  |  |  |  |  |
Plant requirement to meet opacity limit |  |  |  |  |  |  |  | 20.00% |  |  |  |  |  |  |  |
Rule imposes opacity limitation on certain fugitive dust emissions from coal and material handling operations |  |  |  |  |  |  |  | 20.00% |  |  |  |  |  |  |  |
Estimate of possible loss |  |  |  |  |  |  |  | $ 90,400,000 |  |  |  |  |  |  |  |
Clean Air Act Related to Post Combustion Controls [Member] | Public Service Company of New Mexico [Member] | Four Corners Units 4 and 5 (Coal) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  | 13.00% |  |  |  |  |  |  |  |
Clean Power Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of potential extension to submit initial plans to meet environmental targets |  |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |  |
Number of states that filed a petition against the Clean Power Plan | state |  |  |  |  |  |  |  |  |  |  |  | 29 |  |  |  |
Proposed percentage reduction in CO2 emissions | 32.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of time currently remaining to submit initial plans to meet environmental targets | 6 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of time currently remaining to submit initial plans to meet environmental targets, including potential extension | 2 years 6 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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