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Financing - Financing Activities (Details) |  |  |  |  |  |  |  |  |  | 9 Months Ended | 12 Months Ended |  |  |  |  |  |  |
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Oct. 31, 2022 USD ($) derivative | Sep. 30, 2022 USD ($) derivative | Aug. 05, 2022 USD ($) | May 20, 2022 USD ($) | May 02, 2022 USD ($) derivative | Jan. 24, 2022 USD ($) | Jun. 18, 2021 USD ($) | Mar. 09, 2021 USD ($) | Dec. 22, 2020 USD ($) | Sep. 30, 2022 USD ($) derivative | Dec. 31, 2021 USD ($) | Oct. 21, 2022 USD ($) | Jun. 01, 2022 USD ($) derivative | Apr. 27, 2022 USD ($) bond | Aug. 16, 2021 USD ($) | Jul. 14, 2021 USD ($) | May 18, 2021 USD ($) | Mar. 09, 2018 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financing capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 40,000,000 |
Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  |  |  |  |  |  |  |  |  | $ 777,700,000 |  |  |  |  |  |
Interest rate contract | Cash Flow Hedge |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of instruments held | derivative |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |
Variable Rate Debt | Interest rate contract | Cash Flow Hedge |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of instruments held | derivative |  | 2 |  |  | 2 |  |  |  |  | 2 |  |  |  |  |  |  |  |
Term of loan |  | 15 months |  | 19 months | 20 months |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative asset, notional amount |  | $ 200,000,000 |  |  |  |  |  |  |  | $ 200,000,000 |  |  |  |  |  |  |  |
Derivative, notional amount |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed interest rate |  |  |  | 2.52% | 2.65% |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative instruments in hedges, fair value |  | $ 8,600,000 |  |  |  |  |  |  |  | $ 8,600,000 |  |  |  |  |  |  |  |
Variable Rate Debt, Tranche 1 | Interest rate contract | Cash Flow Hedge |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable interest rate |  | 4.17% |  |  |  |  |  |  |  | 4.17% |  |  |  |  |  |  |  |
Derivative asset, notional amount |  | $ 100,000,000 |  |  | $ 150,000,000 |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |
Variable Rate Debt, Tranche 2 | Interest rate contract | Cash Flow Hedge |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable interest rate |  | 4.18% |  |  |  |  |  |  |  | 4.18% |  |  |  |  |  |  |  |
Derivative asset, notional amount |  | $ 100,000,000 |  |  | $ 200,000,000 |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |
PNMR 2020 Delayed-Draw Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  | $ 300,000,000 |  |  |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  |  |  |  |  |  |  | $ 80,000,000 |  |  |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  |  |  |  |  | $ 220,000,000 |  |  |  |  |  |  |  |  |  |
Fixed Rate Debt | Interest rate contract | Cash Flow Hedge | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of instruments held | derivative | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term of loan | 14 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed Rate Debt, Tranche 1 | Interest rate contract | Cash Flow Hedge | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative asset, notional amount | $ 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed interest rate | 4.66% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed Rate, Tranche 2 | Interest rate contract | Cash Flow Hedge | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative asset, notional amount | $ 200,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed interest rate | 4.65% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity term over which financings require regulator approval (more than) |  |  |  |  |  |  |  |  |  | 18 months |  |  |  |  |  |  |  |
PNM | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  |  |  |  |  |  |  |  |  | 400,000,000 |  |  |  |  |  |
Texas-New Mexico Power Company | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining borrowing capacity |  |  |  |  |  |  |  |  |  |  |  | $ 96,500,000 |  |  |  |  |  |
Line of credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ratio of debt to capital (less than or equal to) |  |  |  |  |  |  |  |  |  | 70.00% |  |  |  |  |  |  |  |
Line of credit | PNM 2022 Delayed-Draw Term Loan | Revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financing capacity |  |  | $ 225,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from long-term lines of credit |  | 45,000,000 | $ 180,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit | Variable Rate Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hedging arrangement |  | $ 650,000,000 |  |  |  |  |  |  |  | $ 650,000,000 |  |  |  |  |  |  |  |
Line of credit | PNMR 2021 Delayed-Draw Term Loan | Revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financing capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000,000,000 |
Proceeds from long-term lines of credit |  |  |  |  |  | $ 100,000,000 |  |  |  |  | $ 900,000,000 |  |  |  |  |  |  |
Line of credit | PNM and TNMP |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ratio of debt to capital (less than or equal to) |  |  |  |  |  |  |  |  |  | 65.00% |  |  |  |  |  |  |  |
Bonds | PNMR 2021 Delayed-Draw Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable interest rate |  | 4.13% |  |  |  |  |  |  |  | 4.13% |  |  |  |  |  |  |  |
Bonds | PNM | Pollution Control Revenue Bonds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |  |  |  |  | 104,500,000 |  | $ 31,500,000 |  |  |  |  |
Bonds | PNM | Pollution Control Revenue Bonds Due June Twenty Thirty Eight |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  | $ 36,000,000 |  | 36,000,000 |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  | 1.05% |  |  |  |  |  |  |
Bonds | PNM | Pollution Control Revenue Bonds Due June Twenty Forty |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  | $ 37,000,000 |  | $ 37,000,000 |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  | 2.125% |  |  |  |  |  |  |
Bonds | PNM | Pollution Control Revenue Bonds Due June Twenty Forty, City Of Farmington, NM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  | $ 11,500,000 |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  | 1.20% |  |  |  |  |  |  |
Bonds | PNM | Pollution Control Revenue Bonds Due June Twenty Forty Two |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  | $ 20,000,000 |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  | 2.45% |  |  |  |  |  |  |
Bonds | PNM | Pollution Control Revenue Bonds Due June Twenty Twenty Four |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 3.00% |  |  |  |  |
Bonds | PNM | PNM 2021 75 Million Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable interest rate |  | 3.53% |  |  |  |  |  |  |  | 3.53% |  |  |  |  |  |  |  |
Bonds | Texas-New Mexico Power Company | TNMP 2022 Bond Purchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 160,000,000 |  |  |  |
Debt instrument, series of bond issuance | bond |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |
Bonds | Texas-New Mexico Power Company | TNMP 2022 Bond Purchase Agreement at 4.13% Due May 12, 2022 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 65,000,000 |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.13% |  |  |  |
Bonds | Texas-New Mexico Power Company | TNMP 2022 Bond Purchase Agreement at 3.81% Due July 28, 2032 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 95,000,000 |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.81% |  |  |  |
Mortgage Bonds | Texas-New Mexico Power Company | TNMP 2021 Bond Purchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 65,000,000 | $ 65,000,000 |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.44% |  |  |
Senior Notes | PNM | PNM 2021 Note Purchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 160,000,000 |  |
Senior Notes | PNM | PNM 2021 SUNs At 2.59 Percent Due July 15, 2033 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 80,000,000 |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.59% |  |
Senior Notes | PNM | PNM 2021 SUNs At 3.14 Percent Due July 15, 2041 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 80,000,000 |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.14% |  |
Senior Notes | PNM | PNM 2021 SUNs At 5.35 Percent Due October 1, 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 160,000,000 |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.35% |  |
Senior Notes | PNM | PNM 2019 40 Million Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  | $ 40,000,000 |  |  |  |  |  |  |  |  |  |  |
Term loan agreement with banks | PNM | PNM 2021 75 Million Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  | $ 75,000,000 |  |  |  |  |  |  |  |  |  |  |
Unsecured Debt | PNMR 2018 SUNS 3.25% due March 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 300,000,000
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.25%
Repayments of debt |  |  |  |  |  |  |  | $ 80,000,000 |  |  |  |  |  |  |  |  |  |

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