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Commitments and Contingencies (Details) |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended | 35 Months Ended |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 01, 2016 USD ($) | Dec. 31, 2015 USD ($) MW | Dec. 21, 2015 | Oct. 29, 2015 USD ($) | Aug. 17, 2015 USD ($) | Aug. 13, 2015 USD ($) MWh MW | Jul. 17, 2015 | Mar. 02, 2015 lb / MMBTU T | May. 16, 2014 USD ($) | Dec. 20, 2013 USD ($) $ / kw MW | May. 31, 2010 USD ($) | Jun. 30, 2015 USD ($) | Mar. 31, 2015 USD ($) | Dec. 31, 2015 USD ($) MW | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Jan. 31, 2016 USD ($) | Feb. 09, 2016 | Jan. 26, 2016 state | Dec. 02, 2015 Allotment_Parcel | Oct. 01, 2015 opp | Sep. 30, 2015 opp | Aug. 11, 2015 T | Jul. 31, 2015 MW | Jul. 13, 2015 a | May. 19, 2015 MW | May. 14, 2015 lb / MMBTU | Jan. 22, 2015 Allotment_Parcel | Jan. 07, 2015 MW | Jun. 30, 2014 USD ($) MW | May. 31, 2014 USD ($) | Apr. 02, 2014 Allotment_Parcel | Jan. 06, 2014 Allotment_Parcel | Dec. 30, 2013 lb / Decatherm | Aug. 31, 2013 | May. 23, 2013 USD ($) | Oct. 31, 2012 USD ($) | Sep. 30, 2012 landowner | Aug. 06, 2012 compliance_alternative | Dec. 31, 2011 mw | Jan. 31, 2010 opp | Aug. 31, 2006 USD ($) | Jul. 31, 2005 T | Dec. 31, 2003 | Dec. 31, 1999 state
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant in Service |  | $ 6,307,261,000 |  |  |  |  |  |  |  |  |  |  |  | $ 6,307,261,000 | $ 5,941,581,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Depreciation |  | (2,058,772,000) |  |  |  |  |  |  |  |  |  |  |  | (2,058,772,000) | (1,939,760,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  |  |  |  |  |  |  | 167,471,000 | 1,062,000 | $ 12,235,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reversal of deferred items related to BART at SJGS |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,826,000 | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other current assets |  | 82,104,000 |  |  |  |  |  |  |  |  |  |  |  | 82,104,000 | 58,471,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
San Juan Generating Station [Member] | Continuous Highwall Mining [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed retroactive surface mining royalty rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12.50% |  |  |  |  |  |  |  |  |  |
Surface mining royalty rate applied between 2000 and 2003 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8.00% |
Estimated underpaid surface mining royalties under proposed rate change |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5,000,000 |  |  |
PNM's share of estimated underpaid surface mining royalties under proposed rate change |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 46.30% |  |  |
San Juan Generating Station [Member] | SJCC Arbitration [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential unbilled mining costs owed to SJCC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential overbilled mining costs SJCC owes to SJGS owners |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential capital improvements billed as mining costs to SJGS owners |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 13,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Clean Air Act related to Regional Haze [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [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 Power Plan [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of states that filed a petition against the Clean Power Plan | state |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 29 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed percentage reduction in CO2 emissions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 32.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
San Juan Generating Station Unit 4 [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unsubscribed ownership (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 65 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Third party sale of ownership percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 48.00% |  |  |  |  |  |  |  |  |  |  |
Approved lease extension term |  |  |  |  |  |  | 25 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of time to remedy violations until suit is filed |  |  | 60 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Four Corners [Member] | NMTRD Coal Severance Tax [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assessed coal severance surtax penalty and interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 30,000,000 |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant in Service |  | 4,833,303,000 |  |  |  |  |  |  |  |  |  |  |  | 4,833,303,000 | 4,581,066,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Depreciation |  | (1,569,549,000) |  |  |  |  |  |  |  |  |  |  |  | (1,569,549,000) | (1,486,406,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  |  |  |  |  |  |  | 167,471,000 | 1,062,000 | 12,235,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reversal of deferred items related to BART at SJGS |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,826,000 | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other current assets |  | 74,990,000 |  |  |  |  |  |  |  |  |  |  |  | 74,990,000 | 53,095,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets |  | 342,910,000 |  |  |  |  |  |  |  |  |  |  |  | 342,910,000 | 401,025,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | SPS Complaint, Federal Power Act [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed settlement pending regulatory approval |  |  |  | $ 4,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Portion of proposed settlement to be credited to customers, pending regulatory approval |  |  |  | $ 2,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Navajo Nation Allottee Matters [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of landowners claiming to be Navajo allottees (in landowners) | landowner |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 43 |  |  |  |  |  |  |
Number of allotment parcels' appraisal requested for review (in allotment parcels) | Allotment_Parcel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 58 |  |  |  |  |  |  |  |  |  |  |  |
Number of allotments where landowners are revoking rights of way renewal consents | Allotment_Parcel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of allotments, Previously contested rights of way renewal consents | Allotment_Parcel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acres of land at issue (in acres) | a |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15.49 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of allotment parcels' at issue, Not to be condemned | Allotment_Parcel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of allotment parcels' at issue | Allotment_Parcel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Surface [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets |  | 100,000,000 |  |  |  |  |  |  |  |  |  |  |  | 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | SJCC Arbitration [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM's share of arbitration ruling |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 46.30% |  |  |  |  |  |  |  |  |  |  |  |  |  |
FFPAC percentage of mining costs overbilled or unbilled ruled by arbitration |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 33.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated costs to remain unrecovered |  |  |  |  |  | $ 20,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  |  |  |  |  |  |  | 21,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | National Ambient Air Quality Standards, 2015 EPA Legal Settlement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of time to act on settlement |  |  |  |  |  |  |  | 16 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Emissions tons of SO2 per year | T |  |  |  |  |  |  |  | 16,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | National Ambient Air Quality Standards, 2015 EPA Legal Settlement [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
SO2 emissions rate (in pounds per MMBTU) | lb / MMBTU |  |  |  |  |  |  |  | 0.45 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Emissions tons of SO2 per year | T |  |  |  |  |  |  |  | 2,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | National Ambient Air Quality Standards [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revised SO2 emissions agreed upon (in pounds per MMBTU) | lb / MMBTU |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.10 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Loss on long-term purchase commitment [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual funding post-term reclamation trust |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,300,000 | 1,000,000 | 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Mine Reclamation Trust [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclamation trust funding, next fiscal year |  | 4,900,000 |  |  |  |  |  |  |  |  |  |  |  | 4,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclamation trust funding, year 2 |  | 5,400,000 |  |  |  |  |  |  |  |  |  |  |  | 5,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Mine Reclamation Trust [Member] | Four Corners [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclamation trust funding, next fiscal year |  | 1,900,000 |  |  |  |  |  |  |  |  |  |  |  | 1,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclamation trust funding, year 2 |  | 2,000,000 |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclamation trust funding, year 3 |  | 2,100,000 |  |  |  |  |  |  |  |  |  |  |  | 2,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Loss on long-term purchase commitment [Member] | Surface [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liability for interim storage costs |  | 38,800,000 |  |  |  |  |  |  |  |  |  |  |  | 38,800,000 | 25,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Final reclamation, capped amount to be collected |  |  |  |  |  |  |  |  |  |  |  |  |  | 100,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Loss on long-term purchase commitment [Member] | Underground [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liability for interim storage costs |  | 11,400,000 |  |  |  |  |  |  |  |  |  |  |  | 11,400,000 | 8,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Funding for decommissioning costs in qualified and non-qualified trust funds |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,900,000 | 4,900,000 | $ 4,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated market value of trusts for decommissioning costs |  | $ 249,100,000 |  |  |  |  |  |  |  |  |  |  |  | $ 249,100,000 | 244,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Composite Interest |  | 10.20% |  |  |  |  |  |  |  |  |  |  |  | 10.20% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant in Service |  | $ 562,412,000 |  |  |  |  |  |  |  |  |  |  |  | $ 562,412,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Depreciation |  | (164,549,000) |  |  |  |  |  |  |  |  |  |  |  | (164,549,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Construction Work in Progress |  | $ 38,966,000 |  |  |  |  |  |  |  |  |  |  |  | $ 38,966,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Nuclear Plant [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage in nuclear reactor |  | 10.20% |  |  |  |  |  |  |  |  |  |  |  | 10.20% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum potential assessment per incident |  | $ 38,900,000 |  |  |  |  |  |  |  |  |  |  |  | $ 38,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual payment limitation related to incident |  | 5,800,000 |  |  |  |  |  |  |  |  |  |  |  | 5,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate amount of all risk insurance |  | 2,750,000,000.00 |  |  |  |  |  |  |  |  |  |  |  | 2,750,000,000.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sublimit amount under nuclear electric insurance limited |  | 2,250,000,000.00 |  |  |  |  |  |  |  |  |  |  |  | 2,250,000,000.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum amount under nuclear electric insurance limited |  | 5,400,000 |  |  |  |  |  |  |  |  |  |  |  | 5,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Nuclear Plant [Member] | Commercial Providers [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liability insurance coverage |  | 375,000,000 |  |  |  |  |  |  |  |  |  |  |  | 375,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Nuclear Plant [Member] | Industry Wide Retrospective Assessment Program [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liability insurance coverage |  | 13,100,000,000.0 |  |  |  |  |  |  |  |  |  |  |  | 13,100,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Maximum [Member] | Nuclear Plant [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liability insurance coverage |  | 13,500,000,000 |  |  |  |  |  |  |  |  |  |  |  | 13,500,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Department of energy, spent nuclear fuel removal January 2007 - June 2011 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM's share of third party settlement claim |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Department of energy, spent nuclear fuel removal July 2011 - June 2014 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM's share of third party settlement claim |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Litigation settlement, portion credited to customers |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Department of energy, spent nuclear fuel removal July 2014 - June 2015 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM's share of third party settlement claim |  |  |  |  |  |  |  |  |  |  |  | $ 1,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Litigation settlement, portion credited to customers |  |  |  |  |  |  |  |  |  |  |  | $ 500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Nuclear spent fuel and waste disposal [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss contingency, estimate of possible loss |  | 58,000,000 |  |  |  |  |  |  |  |  |  |  |  | 58,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual fee, nuclear waste disposal |  |  |  |  |  |  |  |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] | Nuclear spent fuel and waste disposal [Member] | Other Deferred Credits [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liability for interim storage costs |  | $ 12,200,000 |  |  |  |  |  |  |  |  |  |  |  | $ 12,200,000 | 12,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Composite Interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 46.30% |  |  |  |  |  |  |  |
Minimum megawatt capacity from coal and oil-fired electric generating units under jurisdiction of the Mercury and Air Toxics Standards (in megawatts) | mw |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25 |  |  |  |  |
Mercury removal efficiency |  | 99.00% |  |  |  |  |  |  |  |  |  |  |  | 99.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Coal Supply [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other current assets |  | $ 49,000,000 |  |  |  |  |  |  |  |  |  |  |  | $ 49,000,000 | $ 37,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated increase in coal cost |  | 40.00% |  |  |  |  |  |  |  |  |  |  |  | 40.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Clean Air Act, SCR [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated total capital cost if requirement occurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 824,000,000 |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Clean Air Act, SCR [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated total capital cost if requirement occurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 910,000,000 |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Overall reduction of ownership (in megawatts) | MW |  |  |  |  |  |  |  |  |  | 340 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Clean Air Act, SNCR [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated installation capital costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 85,000,000 |  |  |  |  |  |  |  |
Estimated portion of total capital costs if requirement occurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 105,000,000 |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Clean Air Act, SNCR [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated installation capital costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90,000,000 |  |  |  |  |  |  |  |
Estimated portion of total capital costs if requirement occurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 110,000,000 |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Mercury Control [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current annual mercury control costs |  |  |  |  |  |  |  |  |  |  | $ 700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Mercury Control [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contingent estimated annual mercury control cost |  |  |  |  |  |  |  |  |  |  | $ 6,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Loss on long-term purchase commitment [Member] | Surface [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss contingency, estimate of possible loss |  | $ 98,200,000 |  |  |  |  |  |  |  |  |  |  |  | $ 98,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  | 16,500,000 |  |  |  |  |  |  |  |  |  |  |  | 16,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Loss on long-term purchase commitment [Member] | Underground [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss contingency, estimate of possible loss |  | 118,900,000 |  |  |  |  |  |  |  |  |  |  |  | 118,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant in Service |  | 468,200,000 |  |  |  |  |  |  |  |  |  |  |  | 468,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Depreciation |  | (193,300,000) |  |  |  |  |  |  |  |  |  |  |  | (193,300,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Construction Work in Progress |  | 2,200,000 |  |  |  |  |  |  |  |  |  |  |  | 2,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net book value |  | $ 277,100,000 |  |  |  |  |  |  |  |  |  |  |  | $ 277,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [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% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] | Increase in coal mine decommissioning liability [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory disallowances and restructuring costs |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 165,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated undepreciated value |  |  |  |  |  | $ 150,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 1 and 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed proportionate ownership share |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 58.70% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 1 and 4 [Member] | Clean Air Act, SNCR [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total costs for SNCRs and BDT equipment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 78,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 1 and 4 [Member] | Clean Air Act, SNCR [Member] | Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated installation capital costs |  |  |  |  |  |  |  |  |  | $ 82,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed proportionate ownership share |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 64.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional ownership to be obtained (in megawatts) | MW |  |  |  |  |  | 65 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 132 |  | 132 |  |  |  | 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% |  |  |  |  |  |  |  |  |  |  |  | 38.80% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  | 38.50% |  |  |  |  |  |  |  |  |  |  |  | 38.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Costs to obtain additional ownership |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] | Clean Air Act, SNCR [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual cost of renewable energy credits, maximum |  |  |  |  |  | $ 7,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 4 [Member] | Clean Air Act, SNCR Hearing Examiner Recommended Denial [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional ownership to be obtained (in megawatts) | MW |  |  |  |  |  | 132 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station Unit 3 [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership held by exiting owners |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Four Corners [Member] | Clean Air Act related to Post-Combustion Controls [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss contingency, estimate of possible loss |  | $ 94,000,000 |  |  |  |  |  |  |  |  |  |  |  | $ 94,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of compliance alternatives | compliance_alternative |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |
Government standard emissions limit (pounds per MMBTU, parts per million) | lb / Decatherm |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 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% |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Four Corners Units 4 and 5 (Coal) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Composite Interest |  | 13.00% |  |  |  |  |  |  |  |  |  |  |  | 13.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant in Service |  | $ 167,874,000 |  |  |  |  |  |  |  |  |  |  |  | $ 167,874,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Depreciation |  | (102,559,000) |  |  |  |  |  |  |  |  |  |  |  | (102,559,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Construction Work in Progress |  | $ 19,390,000 |  |  |  |  |  |  |  |  |  |  |  | $ 19,390,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Four Corners Units 4 and 5 (Coal) [Member] | Clean Air Act related to Post-Combustion Controls [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13.00% |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | Four Corners Units 4 and 5 (Coal) [Member] | Clean Air Act Lawsuit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  | 13.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Litigation settlement, amount |  |  |  |  | $ 1,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Litigation settlement, expected capital spend, environmental |  |  |  |  | $ 6,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station And Four Corners [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed government standard emission limit (in ozone parts per million) | opp |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 60 |  |  |  |
Public Service Company of New Mexico [Member] | San Juan Generating Station And Four Corners [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Government standard emissions limit (pounds per MMBTU, parts per million) | opp |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 70 | 75 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed government standard emission limit (in ozone parts per million) | opp |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 70 |  |  |  |
PNMR and PNM [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts not included in retail rates (in megawatts) | MW |  | 134 |  |  |  |  |  |  |  |  |  |  |  | 134 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNMR and PNM [Member] | Palo Verde Nuclear Generating Station Unit 3 [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of megawatts not included in retail rates (in megawatts) | MW |  |  |  |  |  | 134 |  |  |  | 134 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed value per kilowatt (in dollars per kilowatt) | $ / kw |  |  |  |  |  |  |  |  |  | 2,500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NM Capital [Member] | Subsequent Event [Member] | BTMU Term Loan Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | $ 125,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NM Capital [Member] | San Juan Generating Station [Member] | Subsequent Event [Member] | Coal Supply [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to fund long-tern loans to unaffiliated third party | 125,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan agreement | $ 125,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable interest rate | 7.25% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Coal mine reclamation bonds to be posted with NMMMD | $ 161,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash used to support bank letter or credit arrangement | $ 40,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of days to provide security interest | 180 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNMR Development [Member] | San Juan Generating Station Unit 4 [Member] | Clean Air Act, SNCR [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential acquisition of ownership (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 65 |  | 65 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other income, restructuring fee |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition Annual Fee, Nuclear Waste Disposal + References No definition available. + Details
Name: | pnm_AnnualFeeNuclearWasteDisposal
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Cash used to support bank letter or credit arrangement + References No definition available. + Details
Name: | pnm_Cashusedtosupportbankletterorcreditarrangement
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Coal Mine Reclamation Bonds to be posted with NMMMD + References No definition available. + Details
Name: | pnm_CoalMineReclamationBondstobepostedwithNMMMD
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition coal-fired generation in Megawatts + References No definition available. + Details
Name: | pnm_CoalfiredgenerationinMegawatts
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Contingent Estimated Annual Mercury Control Cost + References No definition available. + Details
Name: | pnm_ContingentEstimatedAnnualMercuryControlCost
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Current Annual Mercury Control Costs + References No definition available. + Details
Name: | pnm_CurrentAnnualMercuryControlCosts
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Effective Income Tax Rate Reconciliation, Reversal of deferred items related to disallowed costs + References No definition available. + Details
Name: | pnm_EffectiveIncomeTaxRateReconciliationReversalofdeferreditemsrelatedtodisallowedcosts
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Estimated Portion of Total Capital Costs if Requirement Occured + References No definition available. + Details
Name: | pnm_EstimatedPortionOfTotalCapitalCostsIfRequirementOccured
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Estimated Total Capital Cost If Requirement Occurred + References No definition available. + Details
Name: | pnm_EstimatedTotalCapitalCostIfRequirementOccurred
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Final Reclamation, capped amount to be collected + References No definition available. + Details
Name: | pnm_FinalReclamationCappedAmountToBeCollected
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Jointly Owned Utility Plan, Proposed Proportionate Ownership Share + References No definition available. + Details
Name: | pnm_JointlyOwnedUtilityPlanProposedProportionateOwnershipShare
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Litigation Settlement, Portion credited to customers + References No definition available. + Details
Name: | pnm_LitigationSettlementPortioncreditedtocustomers
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Litigation settlement, expected capital spend, environmental + References No definition available. + Details
Name: | pnm_Litigationsettlementexpectedcapitalspendenvironmental
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Mercury Removal Rate, Percentage + References No definition available. + Details
Name: | pnm_MercuryRemovalRatePercentage
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Minimum Megawatt Capacity from Coal and Oil-Fired Electric Generating Units under Jurisdiction of the Mercury and Air Toxics Standards + References No definition available. + Details
Name: | pnm_MinimumMegawattCapacityFromCoalAndOilFiredElectricGeneratingUnitsUnderJurisdictionOfMerucyAndAirToxicsStandards
Namespace Prefix: | pnm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Net book value + References No definition available. + Details
Name: | pnm_NetBookValue
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of allotment parcels' appraisal requested for review + References No definition available. + Details
Name: | pnm_Numberofallotmentparcelsappraisalrequestedforreview
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of allotment parcels' at issue + References No definition available. + Details
Name: | pnm_Numberofallotmentparcelsatissue
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of allotment parcels' at issue, Not to be condemned + References No definition available. + Details
Name: | pnm_NumberofallotmentparcelsatissueNottobecondemned
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of allotments, Previously contested rights of way renewal consents + References No definition available. + Details
Name: | pnm_NumberofallotmentsPreviouslycontestedrightsofwayrenewalconsents
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of allotments where landowners are revoking rights of way renewal consents + References No definition available. + Details
Name: | pnm_Numberofallotmentswherelandownersarerevokingrightsofwayrenewalconsents
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of days to provide security interest + References No definition available. + Details
Name: | pnm_Numberofdaystoprovidesecurityinterest
Namespace Prefix: | pnm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of landowners claiming to be Navajo allottees + References No definition available. + Details
Name: | pnm_NumberoflandownersclaimingtobeNavajoallottees
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of states that filed a petition against the Clean Power Plan + References No definition available. + Details
Name: | pnm_NumberofstatesthatfiledapetitionagainsttheCleanPowerPlan
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Other income, restructuring fee + References No definition available. + Details
Name: | pnm_Otherincomerestructuringfee
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition PNMs share of third party settlement claim + References No definition available. + Details
Name: | pnm_PNMsshareofthirdpartysettlementclaim
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Payments to fund long-tern loans to unaffiliated third party + References No definition available. + Details
Name: | pnm_Paymentstofundlongternloanstounaffiliatedthirdparty
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of ownership held by exiting owners + References No definition available. + Details
Name: | pnm_Percentageofownershipheldbyexitingowners
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Period of time to act on settlement + References No definition available. + Details
Name: | pnm_Periodoftimetoactonsettlement
Namespace Prefix: | pnm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Public Utilities, 1-hour SO2 Emissions Rate + References No definition available. + Details
Name: | pnm_PublicUtilities1hourSO2EmissionsRate
Namespace Prefix: | pnm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Additional Ownership To Be Obtained, in Megawatts + References No definition available. + Details
Name: | pnm_PublicUtilitiesAdditionalOwnershipToBeObtainedinMegawatts
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Aggregate Amount of All Risk Insurance + References No definition available. + Details
Name: | pnm_PublicUtilitiesAggregateAmountOfAllRiskInsurance
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Annual Funding post-term reclamation trust + References No definition available. + Details
Name: | pnm_PublicUtilitiesAnnualFundingposttermreclamationtrust
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Public Utilities, Annual Payment Limitation Related to Incident + References No definition available. + Details
Name: | pnm_PublicUtilitiesAnnualPaymentLimitationRelatedToIncident
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Annual cost of Renewable Energy Credits + References No definition available. + Details
Name: | pnm_PublicUtilitiesAnnualcostofRenewableEnergyCredits
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Public Utilities, Approved lease extension term, Years + References No definition available. + Details
Name: | pnm_PublicUtilitiesApprovedleaseextensiontermYears
Namespace Prefix: | pnm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Public Utilities, Assessed Coal Severance Surtax Penalty and Interest + References No definition available. + Details
Name: | pnm_PublicUtilitiesAssessedCoalSeveranceSurtaxPenaltyandInterest
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Costs to obtain additional ownership + References No definition available. + Details
Name: | pnm_PublicUtilitiesCoststoobtainadditionalownership
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Current Surface Mining Royalty Rate applied between 2000 and 2003 + References No definition available. + Details
Name: | pnm_PublicUtilitiesCurrentSurfaceMiningRoyaltyRateappliedbetween2000and2003
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Current ownership interest, in Megawatts + References No definition available. + Details
Name: | pnm_PublicUtilitiesCurrentownershipinterestinMegawatts
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Emissions Tons of SO2 per year + References No definition available. + Details
Name: | pnm_PublicUtilitiesEmissionsTonsofSO2peryear
Namespace Prefix: | pnm_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Estimated Increase in Coal Cost, Percentage + References No definition available. + Details
Name: | pnm_PublicUtilitiesEstimatedIncreaseinCoalCostPercentage
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Estimated Underpaid Surface Mining Royalties under proposed rate change + References No definition available. + Details
Name: | pnm_PublicUtilitiesEstimatedUnderpaidSurfaceMiningRoyaltiesunderproposedratechange
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Estimated costs to remain unrecovered + References No definition available. + Details
Name: | pnm_PublicUtilitiesEstimatedcoststoremainunrecovered
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Estimated rate base value at 1/1/2018 + References No definition available. + Details
Name: | pnm_PublicUtilitiesEstimatedratebasevalueat112018
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Public Utilities, Estimated undepreciated value at 12/31/17 + References No definition available. + Details
Name: | pnm_PublicUtilitiesEstimatedundepreciatedvalueat123117
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Public Utilities, Percentage of PNM Share of mining costs overbilled or unbilled, as ruled by arbitration, that will pass through FFPAC + References No definition available. + Details
Name: | pnm_PublicUtilitiesFFPACPercentageofminingcostsoverbilledorunbilledruledbyarbitration
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Government Standard Emission Limit + References No definition available. + Details
Name: | pnm_PublicUtilitiesGovernmentStandardEmissionLimit
Namespace Prefix: | pnm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Jointly Owned Utility Plant, Third Party Sale of Ownership Percentage + References No definition available. + Details
Name: | pnm_PublicUtilitiesJointlyOwnedUtilityPlantThirdPartySaleofOwnershipPercentage
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Liability Insurance Coverage + References No definition available. + Details
Name: | pnm_PublicUtilitiesLiabilityInsuranceCoverage
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Public Utilities, Maximum Amount under Nuclear Electic Insurance Limited + References No definition available. + Details
Name: | pnm_PublicUtilitiesMaximumAmountUnderNuclearElecticInsuranceLimited
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Maximum Potential Assessment Per Incident + References No definition available. + Details
Name: | pnm_PublicUtilitiesMaximumPotentialAssessmentPerIncident
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Newly Identified Replacement Gas-fired Generation, in Megawatts, December2013 + References No definition available. + Details
Name: | pnm_PublicUtilitiesNewlyIdentifiedReplacementGasfiredGenerationinMegawattsDecember2013
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Newly Identified Replacement Solar Generation, in Megawatts, December2013 + References No definition available. + Details
Name: | pnm_PublicUtilitiesNewlyIdentifiedReplacementSolarGenerationinMegawattsDecember2013
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Number of Compliance alternatives + References No definition available. + Details
Name: | pnm_PublicUtilitiesNumberOfComplianceAlternatives
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Number of States To Address Regional Haze + References No definition available. + Details
Name: | pnm_PublicUtilitiesNumberOfStatesToAddressRegionalHaze
Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Number of Megawatt-hours of Renewable Energy Certificates to be acquired and retired beginning Jan 2020 + References No definition available. + Details
Name: | pnm_PublicUtilitiesNumberofMegawatthoursofRenewableEnergyCertificatestobeacquiredandretiredbeginningJan2020
Namespace Prefix: | pnm_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Number of Megawatts Nuclear Generation + References No definition available. + Details
Name: | pnm_PublicUtilitiesNumberofMegawattsNuclearGeneration
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Overall Reduction Of Ownership, in Megawatts + References No definition available. + Details
Name: | pnm_PublicUtilitiesOverallReductionOfOwnershipinMegawatts
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Ownership Percentage + References No definition available. + Details
Name: | pnm_PublicUtilitiesOwnershipPercentage
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Ownership Percentage in Nuclear Reactor + References No definition available. + Details
Name: | pnm_PublicUtilitiesOwnershipPercentageInNuclearReactor
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, PNM Share Estimated Underpaid Surface Mining Royalties under proposed rate change + References No definition available. + Details
Name: | pnm_PublicUtilitiesPNMShareEstimatedUnderpaidSurfaceMiningRoyaltiesunderproposedratechange
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, PNM Share of arbitration ruling + References No definition available. + Details
Name: | pnm_PublicUtilitiesPNMShareofarbitrationruling
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Period of time to remedy violations until suit is filed, Days + References No definition available. + Details
Name: | pnm_PublicUtilitiesPeriodoftimetoremedyviolationsuntilsuitisfiledDays
Namespace Prefix: | pnm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Public Utilities, Portion of proposed settlement to be credited to customers, pending regulatory approval + References No definition available. + Details
Name: | pnm_PublicUtilitiesPortionofproposedsettlementtobecreditedtocustomerspendingregulatoryapproval
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Public Utilities, Potential Acquisition of Ownership in Megawatts + References No definition available. + Details
Name: | pnm_PublicUtilitiesPotentialAcquisitionofOwnershipinMegawatts
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Potential Capital Improvements billed as Mining Costs to SJGS Owners + References No definition available. + Details
Name: | pnm_PublicUtilitiesPotentialCapitalImprovementsbilledasMiningCoststoSJGSOwners
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Public Utilities, Potential Overbilled Mining Costs SJCC Owes to SJGS Owners + References No definition available. + Details
Name: | pnm_PublicUtilitiesPotentialOverbilledMiningCostsSJCCOwestoSJGSOwners
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Public Utilities, Potential Unbilled Mining Costs Owed to SJCC + References No definition available. + Details
Name: | pnm_PublicUtilitiesPotentialUnbilledMiningCostsOwedtoSJCC
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Potential to emit tons per year of visibility impairing pollution, maximum + References No definition available. + Details
Name: | pnm_PublicUtilitiesPotentialtoemittonsperyearofvisibilityimpairingpollutionmaximum
Namespace Prefix: | pnm_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Proposed Government Standard Emission Limit + References No definition available. + Details
Name: | pnm_PublicUtilitiesProposedGovernmentStandardEmissionLimit
Namespace Prefix: | pnm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Proposed Retroactive Surface Mining Royalty Rate + References No definition available. + Details
Name: | pnm_PublicUtilitiesProposedRetroactiveSurfaceMiningRoyaltyRate
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Proposed percentage reduction in CO2 emissions, Stayed by the USSC + References No definition available. + Details
Name: | pnm_PublicUtilitiesProposedpercentagereductioninCO2emissionsStayedbytheUSSC
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Proposed settlement pending regulatory approval + References No definition available. + Details
Name: | pnm_PublicUtilitiesProposedsettlementpendingregulatoryapproval
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Public Utilities, Proposed value per Kilowatt effective January 1, 2018 + References No definition available. + Details
Name: | pnm_PublicUtilitiesProposedvalueperKilowatteffectiveJanuary12018
Namespace Prefix: | pnm_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Recovery Percentage of Estimated undepreciated value at 12/31/17 + References No definition available. + Details
Name: | pnm_PublicUtilitiesRecoveryPercentageofEstimatedundepreciatedvalueat123117
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Requested Time Period to Recover Retired Units NBV + References No definition available. + Details
Name: | pnm_PublicUtilitiesRequestedTimePeriodtoRecoverRetiredUnitsNBV
Namespace Prefix: | pnm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Public Utilities, Revised SO2 Emissions Agreed Upon + References No definition available. + Details
Name: | pnm_PublicUtilitiesRevisedSO2EmissionsAgreedUpon
Namespace Prefix: | pnm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Rule Imposes Opacity Limitation on Certain Fugitive Dust Emissions From Coal and Material Handling Operations + References No definition available. + Details
Name: | pnm_PublicUtilitiesRuleImposesOpacityLimitationOnCertainFugitiveDustEmissionsFromCoalAndMaterialHandlingOperations
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilities, Sublimit Amount under Nuclear Electric Insurance Limited + References No definition available. + Details
Name: | pnm_PublicUtilitiesSublimitAmountUnderNuclearElectricInsuranceLimited
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Unsubscribed Ownership in Megawatts + References No definition available. + Details
Name: | pnm_PublicUtilitiesUnsubscribedOwnershipinMegawatts
Namespace Prefix: | pnm_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Public Utilitites, Plant Requirment to Meet Opacity Limit, Percentage + References No definition available. + Details
Name: | pnm_PublicUtilititesPlantRequirmentToMeetOpacityLimitPercentage
Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Reclamation Trust Funding, Next fiscal year + References No definition available. + Details
Name: | pnm_ReclamationTrustFundingNextfiscalyear
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Reclamation Trust Funding, Year 2 + References No definition available. + Details
Name: | pnm_ReclamationTrustFundingYear2
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Reclamation Trust Funding, Year 3 + References No definition available. + Details
Name: | pnm_ReclamationTrustFundingYear3
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Regulatory Disallowance + References No definition available. + Details
Name: | pnm_RegulatoryDisallowance
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Area of land held. + References No definition available. + Details
Name: | us-gaap_AreaOfLand
Namespace Prefix: | us-gaap_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | instant

X
- Definition The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
Name: | us-gaap_DecommissioningTrustAssetsAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The proportionate share of interest (percent) in a jointly owned utility plant. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 10.C) -URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 10 -Section C + Details
Name: | us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of judgment or settlement awarded to (against) the entity in respect of litigation. + References No definition available. + Details
Name: | us-gaap_LitigationSettlementAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Reflects the amount of cash required to fully fund agreements to provide advances to borrowers and lessees at interest rates that increase or decrease depending on certain facts or circumstances. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 825 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=51676700&loc=d3e61082-112788 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 825 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=51676700&loc=d3e61044-112788 + Details
Name: | us-gaap_LoansAndLeasesReceivableCommitmentsVariableRates
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The percentage points (also referred to as 'margin') added to the reference rate as stated in the loan agreement and used to compute the variable rate on the loans receivable. For instance, the loan agreement might state that the interest rate the borrower is obligated to pay is the London Interbank Offered Rate (LIBOR) plus three quarters (3/4) of a percentage point adjusted quarterly (each three months). LIBOR in this example is the index or reference rate, 3/4 percentage point is the margin, the reference rate plus the margin is the fully indexed rate. This element would be used to report separately the margin. + References No definition available. + Details
Name: | us-gaap_LoansReceivableBasisSpreadOnVariableRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
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