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Financing - Activities, PNM and TNMP (Details) |  |  |  |  |  |  |  |  |  | 1 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 01, 2017 USD ($) | Nov. 01, 2016 USD ($) | Feb. 01, 2016 USD ($) | Dec. 21, 2015 USD ($) | Aug. 11, 2015 USD ($) | May 08, 2015 USD ($) | Dec. 31, 2014 USD ($) | Jun. 27, 2014 USD ($) | Mar. 05, 2014 USD ($) | Jun. 21, 2016 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Feb. 21, 2017 USD ($) | Dec. 21, 2016 USD ($) loan | Oct. 21, 2016 USD ($) | Sep. 27, 2016 USD ($) | May 20, 2016 USD ($) | Dec. 17, 2015 USD ($) | Sep. 30, 2015 | Jun. 01, 2015 USD ($) | Mar. 09, 2015 USD ($) | Dec. 22, 2014 USD ($) | Jan. 01, 2014 USD ($) | Dec. 09, 2013 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding amount |  |  |  |  |  |  |  |  |  |  | $ 287,100,000 | $ 250,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Amount outstanding |  |  |  |  |  |  |  |  |  |  | 100,000,000 | 50,000,000 | $ 0 |  |  |  |  |  |  |  |  |  |  |  |
Fixed interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.927% |  |  |  |  |
Payment of debt |  |  |  |  |  |  |  |  |  |  | 303,793,000 | 333,066,000 | 125,000,000 |  |  |  |  |  |  |  |  |  |  |  |
PNMR Term Loan Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding amount |  |  |  |  |  |  |  |  |  |  | 0 | 150,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
PNMR 2016 One-Year Term Loan and PNMR 2016 Two-Year Term Loan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of loan agreements (in loans) | loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |
PNMR 2016 One Year Term Loan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding amount |  |  |  |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  | $ 100,000,000.0 |  |  |  |  |  |  |  |  |  |
Variable interest rate |  |  |  |  |  |  |  |  |  |  | 1.60% |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNMR 2016 Two Year Term Loan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan entered into |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100,000,000.0 |  |  |  |  |  |  |  |  |  |
Variable interest rate |  |  |  |  |  |  |  |  |  |  | 1.69% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Level 2 [Member] | Cash Flow Hedging [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value gain (loss, less than) |  |  |  |  |  |  |  |  |  |  | $ (100,000) | 100,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Notes Payable to Banks [Member] | PNMR Term Loan Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000.0 |
Amount outstanding |  |  |  | $ 150,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term Loan and Other Outstanding Debt [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  |  | $ 75,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NM Capital [Member] | San Juan Generating Station [Member] | Coal Supply [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to fund long-term loans to unaffiliated third party |  |  | $ 125,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNMR [Member] | PNMR 2016 Two Year Term Loan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan entered into |  |  |  |  |  |  |  |  |  |  | 100,000,000 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding amount |  |  |  |  |  |  |  |  |  |  | 61,000,000 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Payment of debt |  |  |  |  |  |  |  |  |  |  | $ 271,000,000 | 214,300,000 | 75,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Public Service Company of New Mexico [Member] | NMPRC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requirement to obtain approval for any financing transaction, period of time (more than) |  |  |  |  |  |  |  |  |  |  | 18 months |  |  |  |  |  |  |  |  |  |  |  |  |  |
Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding amount |  |  |  |  |  |  |  |  |  |  | $ 0 | 59,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Payment of debt |  |  |  |  |  |  |  |  |  |  | $ 0 | 0 | $ 50,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  | $ 30,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt-to-capital ratios (less than or equal to) |  |  |  |  |  |  |  |  |  |  | 65.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt-to-capital ratios (less than or equal to) |  |  |  |  |  |  |  |  |  |  | 65.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNMR 2015 Term Loan Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan entered into |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000,000.0 |  |  |  |  |  |  | $ 150,000,000.0 |  |  |
Variable interest rate |  |  |  |  |  |  |  |  |  |  | 1.55% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unsecured Debt [Member] | Senior unsecured notes, 9.25% due 2015 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 118,800,000 |
Stated percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.25% |
Unsecured Debt [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shelf registration statement, capacity of issuance (up to) |  |  |  |  |  |  |  |  |  |  | $ 250,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unsecured Debt [Member] | Public Service Company of New Mexico [Member] | 3.85% due 2025 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  | $ 250,000,000.0 |  |  |  |  |  | $ 250,000,000 | 250,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  | 3.85% |  |  |  |  |  | 3.85% |  |  |  |  |  |  |  |  |  |  |  |  |  |
BTMU Term Loan Agreement [Member] | NM Capital [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan entered into |  |  | $ 125,000,000.0 |  |  |  |  |  |  |  | $ 92,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  | 3.64% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated principal payments |  |  |  |  |  |  |  |  |  |  | $ 42,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
BTMU Term Loan Agreement [Member] | NM Capital [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan entered into |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 82,800,000 |  |  |  |  |  |  |  |  |  |  |
Payment of debt | $ 9,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
BTMU Term Loan Agreement [Member] | NM Capital [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt-to-capital ratio |  |  | 65.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
BTMU Term Loan Agreement [Member] | NM Capital [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt, required quarterly payment |  | $ 5,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Letter of Credit [Member] | PNMR [Member] | Letter or credit, 30 mil JP Morgan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 30,300,000 |  |  |  |  |  |  |  |  |
PNM 2014 Term Loan Agreement [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan entered into |  |  |  |  |  |  |  |  | $ 175,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  | $ 175,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM 2014 Multi-Draw Term Loan Agreement [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan entered into |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 125,000,000.0 |  |
Repayments of debt |  |  |  |  |  |  |  |  |  | $ 125,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding borrowings |  |  |  |  |  | $ 25,000,000.0 | $ 100,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unsecured notes, Pollution control revenue bonds [Member] | Public Service Company of New Mexico [Member] | Senior unsecured note, PCRB Due 2043, at 4 percent [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 39,300,000 |
Unsecured notes, Pollution control revenue bonds [Member] | Public Service Company of New Mexico [Member] | Senior unsecured note, PCRB Due 2043, at 2 point 4 percent [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 39,300,000 |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.40% |  |  |  |
PNM 2016 Term Loan Agreement [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  | 1.36% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 175,000,000.0 |  |  |  |  |  |  |
Pollution Control Bonds [Member] | Public Service Company of New Mexico [Member] | Pollution Control Revenue Bonds 1 Point 875 Percent, due 2021 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.875% |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 146,000,000 |  |  |  |  |  |  |  |
Pollution Control Bonds [Member] | Public Service Company of New Mexico [Member] | Pollution Control Revenue Bonds 1 Point 875 Percent, due 2021, 2016 Series A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 46,000,000 |  |  |  |  |  |  |  |
Pollution Control Bonds [Member] | Public Service Company of New Mexico [Member] | Pollution Control Revenue Bonds 1 Point 875 Percent, due 2021, 2016 Series B [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000.0 |  |  |  |  |  |  |  |
Pollution Control Revenue Bonds [Member] | Texas-New Mexico Power Company [Member] | First Mortgage Bonds Due 2024, Series 2014A, at 4.03% [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.03%
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 80,000,000.0
2011 Term Loan Agreement [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  | $ 50,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
First Mortgage Bonds [Member] | Texas-New Mexico Power Company [Member] | First Mortgage Bonds Due 2024, Series 2014A, at 4.03% [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  |  | $ 80,000,000 | 80,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  | 4.03% |  |  |  |  |  |  |  |  |  |  |  |  |  |
First Mortgage Bonds [Member] | Texas-New Mexico Power Company [Member] | First Mortgage Bonds 3 Point 53 Percent, due 2026, Series 2016A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  |  | $ 60,000,000 | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  | 3.53% |  |  |  |  |  |  |  | 3.53% |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 60,000,000.0 |  |  |  |  |  |

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