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Financing - Financing Activities (Details) |  |  |  |  | 3 Months Ended | 9 Months Ended |  |  |  |  |  |  |  |  |
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May 15, 2023 USD ($) | Nov. 10, 2022 USD ($) | Sep. 30, 2022 USD ($) | Aug. 05, 2022 USD ($) | Sep. 30, 2023 USD ($) $ / shares shares | Jun. 30, 2023 USD ($) $ / shares shares | Mar. 31, 2023 $ / shares shares | Sep. 30, 2023 USD ($) | Sep. 30, 2022 USD ($) | Dec. 31, 2023 USD ($) | Jun. 01, 2023 USD ($) | May 16, 2023 USD ($) | Apr. 28, 2023 USD ($) bond debtInstrument | Dec. 31, 2022 USD ($) | Jun. 01, 2022 USD ($) bond | Apr. 27, 2022 USD ($) bond | Dec. 31, 2021 USD ($) | Jun. 18, 2021 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of long-term debt |  |  |  |  |  |  |  | $ 685,000,000 | $ 179,500,000 |  |  |  |  |  |  |  |  |
Fair value of hedge agreements |  |  |  |  | $ 14,000,000 |  |  | 14,000,000 |  |  |  |  |  |  |  |  |  |
Bank Of America, N.A. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward sale agreement (in shares) | shares |  |  |  |  | 2,283,860 |  | 504,452 |  |  |  |  |  |  |  |  |  |  |
Forward sale agreement (in dollars per share) | $ / shares |  |  |  |  | $ 44.03 |  | $ 48.49 |  |  |  |  |  |  |  |  |  |  |
Wells Fargo Bank, N.A. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward sale agreement (in shares) | shares |  |  |  |  |  |  | 528,082 |  |  |  |  |  |  |  |  |  |  |
Forward sale agreement (in dollars per share) | $ / shares |  |  |  |  |  |  | $ 48.30 |  |  |  |  |  |  |  |  |  |  |
MUFG Securities EMEA plc |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward sale agreement (in shares) | shares |  |  |  |  |  | 1,049,116 |  |  |  |  |  |  |  |  |  |  |  |
Forward sale agreement (in dollars per share) | $ / shares |  |  |  |  |  | $ 45.49 |  |  |  |  |  |  |  |  |  |  |  |
Other Current Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of hedge agreements |  |  |  |  | $ 4,000,000 |  |  | 4,000,000 |  |  |  |  |  |  |  |  |  |
Other Deferred Costs Net Including Deferred Finance Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of hedge agreements |  |  |  |  | 10,000,000 |  |  | 10,000,000 |  |  |  |  |  |  |  |  |  |
At-The-Market |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution agreement |  | $ 200,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, authorized |  |  |  |  |  |  |  | $ 200,000,000 |  |  |  |  |  |  |  |  |  |
PNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity term over which financings require regulator approval (more than) |  |  |  |  |  |  |  | 18 months |  |  |  |  |  |  |  |  |  |
Repayments of long-term debt |  |  |  |  |  |  |  | $ 185,000,000 | $ 179,500,000 |  |  |  |  |  |  |  |  |
Number of debt issuances | bond |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |
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 | $ 225,000,000 |  |  | $ 225,000,000 |  |  |  |  |  |  |  |  |  |
Proceeds from long-term lines of credit |  |  | $ 45,000,000 | $ 180,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit | PNM and TNMP |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ratio of debt to capital (less than or equal to) |  |  |  |  |  |  |  | 65.00% |  |  |  |  |  |  |  |  |  |
Unsecured Debt | PNM, Due May 2026 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  | $ 650,000,000 |  |  |  |  |  |
Unsecured Debt | PNM 3.15% Senior Unsecured Notes, Due May 2023 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.15% |  |  |  |
Repayments of long-term debt | $ 55,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unsecured Debt | PNM | PNM 3.15% Senior Unsecured Notes, Due May 2023 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 55,000,000 |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.15% |  |  |  |
Unsecured Debt | PNM | PNM 2023 Note Purchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 200,000,000 |  |  |  |  |
Number of debt issuances | debtInstrument |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |
Unsecured Debt | PNM | PNM 2023 SUNs At 5.1%, Due April 28, 2035 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000,000 |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 5.51% |  |  |  |  |
Unsecured Debt | PNM | PNM 2023 SUNs At 5.92%, Due April 28, 2053 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 50,000,000 |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 5.92% |  |  |  |  |
Secured Debt | PNM 2023 Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  | $ 500,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Variable rate |  |  |  |  |  |  | 6.77% |  |  |  |  |  |  |  |  |  |  |
Secured Debt | PNM | TNMP 2023 Bond Purchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, series of bond issuance | bond |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |
Secured Debt | Texas-New Mexico Power Company | TNMP 2023 Bond Purchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 185,000,000 |  |  |  |  |
Secured Debt | Texas-New Mexico Power Company | TNMP 2023 Bond Purchase Agreement At 5.01%, Due April 28, 2033 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 130,000,000.0 |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 5.01% |  |  |  |  |
Secured Debt | Texas-New Mexico Power Company | TNMP 2023 Bond Purchase Agreement At 5.47%, Due July 28, 2053 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 55,000,000.0 |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 5.47% |  |  |  |  |
Bonds | PCRB 1.10%, Due June 2040 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 130,000,000 |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.10% |  |  |  |
Bonds | PCRB 3.90%, Due June 2028 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  | $ 130,000,000 |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  | 3.90% |  |  |  |  |  |  |
Bonds | PNMR 2021 Delayed-Draw Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable interest rate |  |  |  |  | 6.37% |  |  | 6.37% |  |  |  |  |  |  |  |  |  |
Bonds | PNMR 2023 Delayed-Draw Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable interest rate |  |  |  |  | 6.77% |  |  | 6.77% |  |  |  |  |  |  |  |  |  |
Bonds | PNM | PCRB's |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 31,500,000 |  | $ 104,500,000 |
Bonds | PNM | PCRB, 1.05%, Due January 2038 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.05% |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 36,000,000 |
Bonds | PNM | PCRB, 2.125% Due June 2040 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.125% |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 37,000,000 |
Bonds | PNM | PCRB, 1.20% Due June 2040 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.20% |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 11,500,000 |
Bonds | PNM | PCRB, 2.45% Due September 2042 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.45% |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 20,000,000 |
Bonds | PNM | PCRB, 3.00% Due June 2024 (1) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 36,000,000 |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.00% |  |  |
Bonds | PNM | PCRB, 3.00% Due June 2024 (2) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 37,000,000 |  |  |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.00% |  |  |
Bonds | PNM | PNM 2021 75 Million Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Variable interest rate |  |  |  |  | 6.18% |  |  | 6.18% |  |  |  |  |  |  |  |  |  |
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% |  |
Term loan agreement with banks | PNM | PNM 2021 75 Million Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 75,000,000
Bonds | ETBC I | Securitized Bonds | Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  | $ 343,200,000 |  |  |  |  |  |  |  |

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- Definition Debt Instrument, Covenant, Debt To Capitalization Ratio + References No definition available. + Details
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Namespace Prefix: | pnm_
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Balance Type: | na
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- Definition Debt Instrument, Number Of Debt Issuances + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
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- Definition Debt Instrument, Series Of Bond Issuance + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:integerItemType
Balance Type: | na
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- Definition Public Utilities, Maturity Term Over Which Financings Require Regulator Approval + References No definition available. + Details
Name: | pnm_PublicUtilitiesMaturityTermOverWhichFinancingsRequireRegulatorApproval
Namespace Prefix: | pnm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Sale Of Stock, Amount Authorized + References No definition available. + Details
Name: | pnm_SaleOfStockAmountAuthorized
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Sale Of Stock, Distribution Agreement, Aggregate Value + References No definition available. + Details
Name: | pnm_SaleOfStockDistributionAgreementAggregateValue
Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Fair value of all asset derivatives designated as cash flow hedging instruments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480434/815-10-50-4B + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
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