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Commitments and Contingencies (Commitments and Contingencies Related to the Environment) (Details) (USD $) In Millions, unless otherwise specified |  |  |  |  |  |  | 12 Months Ended |  | 12 Months Ended |  |  |  |  | 6 Months Ended |  |  |
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Dec. 21, 2011 mw | Dec. 21, 2011 San Juan Generating Station [Member] | Oct. 31, 2012 San Juan Generating Station [Member] Public Service Company of New Mexico [Member] | Jun. 30, 2013 San Juan Generating Station Units 1 and 4 [Member] Public Service Company of New Mexico [Member] | Jun. 30, 2013 San Juan Generating Station Units 2 and 3 [Member] PNM [Member] | Nov. 08, 2010 Four Corners [Member] | Jun. 30, 2013 Clean Air Act related to Regional Haze [Member] state | Jun. 30, 2013 Clean Air Act Related to Post Combustion Controls [Member] Four Corners [Member] Public Service Company of New Mexico [Member] | Aug. 06, 2012 Clean Air Act Related to Post Combustion Controls [Member] Four Corners [Member] Public Service Company of New Mexico [Member] compliance_alternative | Sep. 30, 2012 Mercury Control [Member] San Juan Generating Station [Member] Public Service Company of New Mexico [Member] | Jan. 31, 2010 Minimum [Member] San Juan Generating Station And Four Corners [Member] Public Service Company of New Mexico [Member] opp | Jan. 31, 2010 Maximum [Member] San Juan Generating Station And Four Corners [Member] Public Service Company of New Mexico [Member] opp | Sep. 30, 2012 Maximum [Member] Mercury Control [Member] San Juan Generating Station [Member] Public Service Company of New Mexico [Member] | Oct. 31, 2012 Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] Minimum [Member] Clean Air Act, SNCR [Member] San Juan Generating Station [Member] Public Service Company of New Mexico [Member] | Jun. 30, 2013 Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] Minimum [Member] Clean Air Act, SNCR [Member] San Juan Generating Station Units 1 and 4 [Member] Public Service Company of New Mexico [Member] | Oct. 31, 2012 Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] Maximum [Member] Clean Air Act, SNCR [Member] San Juan Generating Station [Member] Public Service Company of New Mexico [Member] | Jun. 30, 2013 Installation Costs Including Construction Management, Gross Receipts Taxes, AFUDC, and Other PNM Costs [Member] Maximum [Member] Clean Air Act, SNCR [Member] San Juan Generating Station Units 1 and 4 [Member] Public Service Company of New Mexico [Member] | Jun. 30, 2013 Environmental Protection Agency [Member] WildEarth Guardians filed an action to challenge EPA's rule in the Tenth Circuit [Member] San Juan Generating Station [Member] | Jun. 30, 2013 Environmental Protection Agency [Member] Clean Air Act Related to Post Combustion Controls [Member] Four Corners [Member] Public Service Company of New Mexico [Member] | Dec. 31, 2012 Nuclear Spent Fuel And Waste Disposal [Member] Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member] | Jun. 30, 2013 Nuclear Spent Fuel And Waste Disposal [Member] Other Deferred Credits [Member] Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member] | Dec. 31, 2012 Nuclear Spent Fuel And Waste Disposal [Member] Other Deferred Credits [Member] Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member]
Public Utilities, Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingency, Estimate of Possible Loss |  |  |  |  |  |  |  | $ 75.0 |  |  |  |  |  |  |  |  |  |  |  | $ 42.8 |  |
Public Utilities, Number of Compliance alternatives |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Number of States To Address Regional Haze |  |  |  |  |  |  | 50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Potential to emit tons per year of visibility impairing pollution, maximum |  |  |  |  |  |  | 250 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated Total Capital Cost If Requirement Occured |  |  |  |  |  |  |  |  |  |  |  |  |  | 824 |  | 910 |  |  |  |  |  |
Estimated Installation Capital Costs |  |  |  |  |  |  |  |  |  |  |  |  |  | 85.0 | 60.0 | 90.0 | 80.0 |  |  |  |  |
Estimated Portion of Total Capital Costs if Requirement Occured |  |  |  |  |  |  |  |  |  |  |  |  |  | 105 |  | 110 |  |  |  |  |  |
Jointly Owned Utility Plant, Proportionate Ownership Share |  |  | 46.30% | 52.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
estimated cost of replacing gas fired peaking capacity due to retirement of SJGS units |  |  |  |  | 280 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net book value |  |  |  |  | 289 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Government Standard Emission Limit |  |  |  |  |  |  |  |  |  |  | 0.060 | 0.070 |  |  |  |  |  |  |  |  |  |
Public Utilitites, Plant Requirment to Meet Opacity Limit, Percentage |  |  |  |  |  |  |  | 20.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Rule Imposes Opacity Limitation on Certain Fugitive Dust Emissions From Coal and Material Handling Operations |  |  |  |  |  |  |  | 20.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current Annual Mercury Control Costs |  |  |  |  |  |  |  |  |  | 0.6 |  |  |  |  |  |  |  |  |  |  |  |
Contingent Estimated Annual Mercury Control Cost |  |  |  |  |  |  |  |  |  |  |  |  | 6.1 |  |  |  |  |  |  |  |  |
Minimum Megawatt Capacity from Coal and Oil-Fired Electric Generating Units under Jurisdiction of the Merucy and Air Toxics Standards | 25 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mercury Removal Rate, Percentage |  | 0.99 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Proposed Seeking Shorter Compliance Period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |
Public Utilities, Number of years after issuance of final determination to achieve compliance with requirements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |
Loss Contingency Accrual, at Carrying Value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 12.3 | $ 13.9
Public Utilties, Jointly Owned Utility Plant, Sale of Ownership Percentage |  |  |  |  |  | 48.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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