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Regulatory and Rate Matters - PNM (Details) - Public Service Company of New Mexico [Member] $ in Millions |  |  |  | 3 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 16, 2016 USD ($) | Aug. 27, 2015 USD ($) | Mar. 20, 2015 USD ($) party | Mar. 31, 2016 USD ($) turbine MW | Mar. 31, 2015 USD ($) | Dec. 31, 2015 | Apr. 15, 2016 USD ($) GWh | Jun. 30, 2015 MW | Dec. 31, 2013 | Mar. 01, 2013 | Dec. 31, 2012 USD ($)
Clean Air Act, SNCR [Member] | San Juan Generating Station Units 2 and 3 [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Newly identified replacement gas-fired generation (in megawatts) | MW |  |  |  | 80 |  |  |  | 187 |  |  |
Number of aeroderviative units (in turbines) | turbine |  |  |  | 2 |  |  |  |  |  |  |
Replacement gas-fired aeroderivative generation (in megawatts) | MW |  |  |  | 40 |  |  |  |  |  |  |
Cost of replacement gas-fired unit |  |  |  | $ 86.8 |  |  |  |  |  |  |
2015 Electric Rate Case [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Requested rate increase (decrease) |  | $ 123.5 |  |  |  |  |  |  |  |  |
Requested return on equity |  | 10.50% |  |  |  |  |  |  |  |  |
Renewable Portfolio Standard [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Reasonable cost threshold |  |  |  | 3.00% |  |  |  |  | 3.00% |  |
Renewable Portfolio Standard [Member] | Wind Energy [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Required percentage of diversification |  |  |  | 30.00% |  |  |  |  |  |  |
Renewable Portfolio Standard [Member] | Solar Energy [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Required percentage of diversification |  |  |  | 20.00% |  |  |  |  |  |  |
Renewable Portfolio Standard [Member] | Distributed Generation [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Required percentage of diversification |  |  |  | 3.00% |  |  |  |  |  |  |
Renewable Portfolio Standard [Member] | Renewable Technologies [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Required percentage of diversification |  |  |  | 5.00% |  |  |  |  |  |  |
Renewable Portfolio Standard [Member] | Required Percentage by 2011 [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Required percentage of renewable energy in portfolio to electric sales |  |  |  | 10.00% |  |  |  |  |  |  |
Renewable Portfolio Standard [Member] | Required Percentage by 2015 [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Required percentage of renewable energy in portfolio to electric sales |  |  |  | 15.00% |  |  |  |  |  |  |
Renewable Portfolio Standard [Member] | Required Percentage by 2020 [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Required percentage of renewable energy in portfolio to electric sales |  |  |  | 20.00% |  |  |  |  |  |  |
Renewable Energy Rider [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Approved return on equity |  |  |  | 10.50% |  | 10.50% |  |  |  |  |
Proposal to collect funds under renewable energy procurement plan |  |  |  | $ 42.4 |  |  |  |  |  |  |
2017 Energy Efficiency and Load Management Program [Member] | Subsequent Event [Member] | Disincentives / Incentives Adder [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Program portfolio's total budget | $ 28.0 |  |  |  |  |  |  |  |  |  |
Incentive based on target savings |  |  |  |  |  |  | $ 2.4 |  |  |  |
Targeted savings (in gigawatt hours) | GWh |  |  |  |  |  |  | 75 |  |  |  |
Integrated Resource Plan, 2011 [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Frequency of IRP filings |  |  |  | 3 years |  |  |  |  |  |  |
Planning period covered of IRP |  |  |  | 20 years |  |  |  |  |  |  |
Advanced Metering Infrastructure Costs [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Estimated costs to be recovered |  |  |  | $ 87.2 |  |  |  |  |  |  |
Estimated future investment |  |  |  | $ 33.0 |  |  |  |  |  |  |
Formula Transmission Rate Case [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Amount of regulatory costs not yet approved |  |  |  |  |  |  |  |  |  |  | $ 3.2
Return on equity |  |  | 10.00% |  |  |  |  |  |  |  | 10.81%
Percentage ownership of EIP transmission line |  |  |  |  |  |  |  |  |  | 60.00% |
Number of other parties entered into settlement agreement | party |  |  | 5 |  |  |  |  |  |  |  |
Approved rate increase (decrease) |  |  | $ 1.3 |  |  |  |  |  |  |  |
Firm Requirements Wholesale Power Rate Case, Navopache [Member] [Member] |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of megawatts served under a short-term coordination tariff | MW |  |  |  | 10 |  |  |  |  |  |  |
Revenues from NEC |  |  |  | $ 5.4 | $ 7.1 |  |  |  |  |  |

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