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Financing - Activities, PNM and TNMP (Details) - USD ($) |  |  |  |  |  |  |  |  |  | 12 Months Ended |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 01, 2016 | Dec. 21, 2015 | Aug. 11, 2015 | May. 08, 2015 | Jun. 27, 2014 | Apr. 22, 2013 | Apr. 03, 2013 | Dec. 27, 2012 | Sep. 30, 2011 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 17, 2015 | Sep. 30, 2015 | Jun. 01, 2015 | Mar. 09, 2015 | Dec. 22, 2014 | Mar. 05, 2014 | Dec. 09, 2013 | Mar. 06, 2013 | Dec. 14, 2012
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term debt |  |  |  |  |  |  |  |  |  | $ 250,600,000 | $ 105,600,000 |  |  |  |  |  |  |  |  |  |
Amount borrowed under agreement |  |  |  |  |  |  |  |  |  | 50,000,000 | 0 | $ 0 |  |  |  |  |  |  |  |  |
Fixed interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.927% |  |  |  |  |  |  |
Repayments of unsecured debt |  |  |  |  |  |  |  |  |  |  |  | 26,900,000 |  |  |  |  |  |  |  |  |
Gain (loss) on reacquired debt |  |  |  |  |  |  |  |  |  | 0 | 0 | (3,253,000) |  |  |  |  |  |  |  |  |
NM Capital [Member] | San Juan Generating Station [Member] | Coal Supply [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to fund long-tern loans to unaffiliated third party | $ 125,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term debt |  |  |  |  |  |  |  |  |  | 59,000,000 | 5,000,000 |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000 |
Repayments of debt |  |  |  |  | $ 30,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash offered for debt exchanged |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 140 |
Level 2 [Member] | Cash Flow Hedging [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value gain |  |  |  |  |  |  |  |  |  | 100,000 |  |  |  |  |  |  |  |  |  |  |
PNMR Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term debt |  |  |  |  |  |  |  |  |  | 41,600,000 | 600,000 |  |  |  |  |  |  |  |  |  |
Notes Payable to Banks [Member] | PNMR Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayment of borrowings made under the Revolving Credit Facility |  |  |  |  |  | $ 75,000,000.0 |  | $ 100,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |
PNMR Term Loan Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term debt |  |  |  |  |  |  |  |  |  | $ 150,000,000 | $ 100,000,000 |  |  |  |  |  |  |  |  |  |
PNMR Term Loan Agreement [Member] | Notes Payable to Banks [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000.0
Amount borrowed under agreement |  | $ 150,000,000.0 |  |  |  |  |  | $ 100,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |
PNM Term Loan Agreement [Member] | Notes Payable to Banks [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term debt |  |  |  |  |  | $ 75,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ratio of debt to capital, maximum |  |  |  |  |  |  |  |  |  | 65.00% |  |  |  |  |  |  |  |  |  |  |
Line of Credit [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ratio of debt to capital, maximum |  |  |  |  |  |  |  |  |  | 65.00% |  |  |  |  |  |  |  |  |  |  |
PNMR 2015 Term Loan Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000,000.0 |  |  |  |  |
Variable interest rate |  |  |  |  |  |  |  |  |  | 1.22% |  |  |  |  |  |  |  |  |  |  |
Senior unsecured notes, 9.25% due 2015 [Member] | Senior unsecured notes, 9.25% due 2015 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  | $ 23,800,000 |  |  |  |  |  |  |  |  |
Unsecured Debt [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  |  | 9.25% |  |  |  |  |  |  |  |  |
Unsecured Debt [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shelf registration statement of unsecured debt |  |  |  |  |  |  |  |  |  | $ 250,000,000 |  |  |  |  |  |  |  |  |  |  |
Unsecured Debt [Member] | Senior unsecured notes, 9.25% due 2015 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  | 9.25% |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  |  | $ 118,800,000 |  |  |  |  |  |  |  |  |  |
Unsecured Debt [Member] | 3.85% due 2025 [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  | 3.85% |  |  |  |  |  |  | 3.85% | 3.85% |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  | $ 250,000,000.0 |  |  |  |  |  |  | $ 250,000,000 | $ 0 |  |  |  |  |  |  |  |  |  |
BTMU Term Loan Agreement [Member] | NM Capital [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | $ 125,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM 2014 Term Loan Agreement [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 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] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |  |  |  | $ 125,000,000 |  |  |  |  |  |  | $ 125,000,000.0 |  |  |  |
Variable interest rate |  |  |  |  |  |  |  |  |  | 0.99% |  |  |  |  |  |  |  |  |  |  |
Outstanding borrowings |  |  |  | $ 25,000,000 |  |  |  |  |  |  | 100,000,000.0 |  |  |  |  |  |  |  |  |  |
Unsecured notes, Pollution control revenue bonds [Member] | Senior unsecured note, PCRB Due 2043, at 4 percent [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  |  | $ 39,300,000 |  |  |  |  |  |  |  |  |  |
Unsecured notes, Pollution control revenue bonds [Member] | Senior unsecured note, PCRB Due 2043, at 2 point 4 percent [Member] | Public Service Company of New Mexico [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.40% |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 39,300,000 |  |  |  |  |  |
2011 Term Loan Agreement [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  | $ 50,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from bank debt |  |  |  |  |  |  |  |  | $ 50,000,000 |  |  |  |  |  |  |  |  |  |  |  |
First Mortgage Bonds [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate cash paid for debt exchanged |  |  |  |  |  |  | $ 13,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
First Mortgage Bonds [Member] | First Mortgage Bonds Due 2014, Series 2009A, at 9.50% [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  | $ 93,200,000 |  |  |  |  |  |  |  |  |  |  |  |  | $ 265,500,000 |
Stated percentage |  |  |  |  |  |  | 9.50% |  |  | 9.50% | 9.50% |  |  |  |  |  |  |  |  | 9.50% |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  | $ 172,302,000 | $ 172,302,000 |  |  |  |  |  |  |  |  |  |
First Mortgage Bonds [Member] | First Mortgage Bonds 6.95%, due 2043, Series 2013A [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  | $ 93,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  | 6.95% |  |  | 6.95% | 6.95% |  |  |  |  |  |  |  |  | 6.95% |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  | $ 93,198,000 | $ 93,198,000 |  |  |  |  |  |  |  |  |  |
Unamortized premium |  |  |  |  |  |  | $ 23,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
First Mortgage Bonds [Member] | First Mortgage Bonds Due 2024, Series 2014A, at 4.03% [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  | 4.03% | 4.03% |  |  |  |  |  |  |  |  |  |
Aggregate outstanding principal amount |  |  |  |  |  |  |  |  |  | $ 80,000,000 | $ 80,000,000 |  |  |  |  |  |  |  |  |  |
First Mortgage Bonds [Member] | First Mortgage Bonds 3 Point 53 Percent, due 2026, Series 2016A [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 60,000,000.0 |  |  |  |  |  |  |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  |  |  | 3.53% |  |  |  |  |  |  |  |
Pollution Control Revenue Bonds [Member] | First Mortgage Bonds Due 2024, Series 2014A, at 4.03% [Member] | Texas-New Mexico Power Company [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 80,000,000.0 |  |
Stated percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.03% |  |

X
- Definition Debt Instrument, Cash Offered for Debt Exchanged + References No definition available. + Details
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Balance Type: | credit
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- Definition Debt Instrument, Cash Paid for Debt Exchanged + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
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- Definition Debt Instrument, Shelf Registration Statement for Unsecured Debt + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- 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

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- Definition Ratio of debt to capital, maximum + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399 + Details
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- Definition Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399 + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Definition The amount of debt premium that was originally recognized at the issuance of the instrument that has yet to be amortized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Fixed interest rate related to the interest rate derivative. + References No definition available. + Details
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Data Type: | num:percentItemType
Balance Type: | na
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