Fair Value of Derivative and Other Financial Instruments - Defined Benefit Plans Disclosure (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
PNM | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	$ 407,211	$ 410,463	$ 576,707
PNM | Pension Plan | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	407,717
PNM | Pension Plan | Participation in PNMR Master Trust Investments: | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount		409,970
PNM | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	73,392	70,301	95,805
PNM | Other Postretirement Benefits | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	73,383
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	342,296	342,183
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount		70,704
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	2,419	1,703
PNM | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	47,674	69,001
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	136,474	143,911
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount		43,771
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	2,419	1,703
PNM | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	43,703	42,068
PNM | Significant Other Observable Inputs (Level 2) | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	205,822	198,272
PNM | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount		26,933
PNM | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	0	0
PNM | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	3,971	26,933
PNM | Fair Value Measured at Net Asset Value Per Share | Pension Plan | Uncategorized Investment | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	65,421	67,787
PNM | Fair Value Measured at Net Asset Value Per Share | Other Postretirement Benefits | Uncategorized Investment | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	23,290
TNMP | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	41,353	43,447	62,942
TNMP | Pension Plan | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	41,128
TNMP | Pension Plan | Participation in PNMR Master Trust Investments: | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount		44,050
TNMP | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	8,353	8,718	$ 12,593
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	35,870	38,617
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount		8,722
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	50,093
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	162	149
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	8,241	8,573
TNMP | Fair Value, Inputs, Level 1, 2 and 3 | Other Postretirement Benefits | Investments Categorized Within Fair Value Hierarchy | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	8,403
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	12,192	13,556
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount		8,167
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	46,122
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	162	149
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	7,806	8,018
TNMP | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Postretirement Benefits | Investments Categorized Within Fair Value Hierarchy | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	7,968
TNMP | Significant Other Observable Inputs (Level 2) | Pension Plan | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	23,678	25,061
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount		555
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Participation in PNMR Master Trust Investments: | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	3,971
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Cash and cash equivalents | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	0	0
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Mutual funds | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	435	555
TNMP | Significant Other Observable Inputs (Level 2) | Other Postretirement Benefits | Investments Categorized Within Fair Value Hierarchy | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	435
TNMP | Fair Value Measured at Net Asset Value Per Share | Pension Plan | Uncategorized Investment | Estimate of Fair Value Measurement | Measured on a recurring basis
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	5,258	5,433
PNMR
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	$ 448,845	$ 454,020
PNMR | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List]	Fair Value Measured at Net Asset Value Per Share	Fair Value Measured at Net Asset Value Per Share
PNMR | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List]	Fair Value Measured at Net Asset Value Per Share	Fair Value Measured at Net Asset Value Per Share
PNMR | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List]	Fair Value Measured at Net Asset Value Per Share	Fair Value Measured at Net Asset Value Per Share
PNMR | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	$ 378,166	$ 380,800
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	13,995	17,106
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Corporate stocks, common
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	27,167	53,661
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Corporate stocks, preferred
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	741	639
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	159,281	135,200
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | U.S. government
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	61,684	62,637
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | International government
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	4,713	3,318
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Municipals
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	5,071	4,922
PNMR | Fair Value, Inputs, Level 1, 2 and 3 | Corporate and other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	105,514	103,317
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	148,666	157,467
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	13,995	17,106
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate stocks, common
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	27,167	53,661
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate stocks, preferred
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	741	639
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	49,219	27,412
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. government
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	57,544	58,649
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | International government
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	0	0
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipals
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	0	0
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate and other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	0	0
PNMR | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	229,500	223,333
PNMR | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	0	0
PNMR | Significant Other Observable Inputs (Level 2) | Corporate stocks, common
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	0	0
PNMR | Significant Other Observable Inputs (Level 2) | Corporate stocks, preferred
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	0	0
PNMR | Significant Other Observable Inputs (Level 2) | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	110,062	107,788
PNMR | Significant Other Observable Inputs (Level 2) | U.S. government
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	4,140	3,988
PNMR | Significant Other Observable Inputs (Level 2) | International government
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	4,713	3,318
PNMR | Significant Other Observable Inputs (Level 2) | Municipals
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	5,071	4,922
PNMR | Significant Other Observable Inputs (Level 2) | Corporate and other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	105,514	103,317
PNMR | Fair Value Measured at Net Asset Value Per Share | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	5,617	6,691
PNMR | Fair Value Measured at Net Asset Value Per Share | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	35,137	33,258
PNMR | Fair Value Measured at Net Asset Value Per Share | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	$ 29,925	$ 33,271