Financing - Short-term Debt and Liquidity (Details)		12 Months Ended
	Mar. 11, 2022 USD ($) extension_option	Dec. 31, 2017 USD ($) derivative	Apr. 21, 2022 USD ($)	Mar. 31, 2022 USD ($)	Mar. 10, 2022 USD ($)	Jan. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 23, 2021
Short-term Debt [Line Items]
Financing capacity						$ 40,000,000
Letters of credit outstanding				$ 3,400,000
Notes payable, related parties				$ 6,300,000			$ 6,400,000
Variable Rate Short-Term Debt
Short-term Debt [Line Items]
Term of derivatives		4 years
Aggregate principal amount		$ 50,000,000
PNM Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end				1.70%
PNMR Revolving Credit Facility | WEB LOC Facility
Short-term Debt [Line Items]
Letters of credit outstanding				$ 30,300,000
PNM
Short-term Debt [Line Items]
Letters of credit outstanding				0
Notes payable, related parties				0			0
PNM | Lines of credit
Short-term Debt [Line Items]
NMPRC approved credit facility				40,000,000
PNM | Senior Unsecured Notes PCRB, Reprice Date of June 2022 | Senior Unsecured Notes, Pollution Control Revenue Bonds
Short-term Debt [Line Items]
Unsecured long-term debt, noncurrent				104,500,000
PNM | PNM 2017 New Mexico Credit Facility
Short-term Debt [Line Items]
Letters of credit outstanding				0
TNMP
Short-term Debt [Line Items]
Letters of credit outstanding				0
Notes payable, related parties				$ 700,000			0
TNMP | TNMP Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end				1.25%
PNMR Development
Short-term Debt [Line Items]
Notes payable, related parties				$ 0			$ 0
PNMR Development | PNMR Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end				1.95%
Revolving credit facility
Short-term Debt [Line Items]
Financing capacity				$ 300,000,000
Revolving credit facility | PNM
Short-term Debt [Line Items]
Financing capacity				400,000,000
Revolving credit facility | TNMP
Short-term Debt [Line Items]
Financing capacity	$ 100,000,000				$ 75,000,000
Revolving credit facility | TNMP | First mortgage bonds
Short-term Debt [Line Items]
Collateral amount				$ 75,000,000
Number of extension options | extension_option	2
Extension option period	1 year
Interest rate contract
Short-term Debt [Line Items]
Number of derivatives | derivative		3
Interest rate 1 | Variable Rate Short-Term Debt
Short-term Debt [Line Items]
Fixed interest rate		1.926%						1.926%
Interest rate 2 | Variable Rate Short-Term Debt
Short-term Debt [Line Items]
Fixed interest rate		1.823%
Interest rate 3 | Variable Rate Short-Term Debt
Short-term Debt [Line Items]
Fixed interest rate		1.629%
Subsequent event
Short-term Debt [Line Items]
Notes payable, related parties			$ 6,300,000
Remaining borrowing capacity			705,500,000
Subsequent event | PNMR
Short-term Debt [Line Items]
Remaining borrowing capacity			265,500,000
Consolidated invested cash			900,000
Subsequent event | PNM
Short-term Debt [Line Items]
Notes payable, related parties			0
Remaining borrowing capacity			400,000,000
Consolidated invested cash			8,700,000
Subsequent event | PNM | Lines of credit
Short-term Debt [Line Items]
Remaining borrowing capacity			40,000,000
Subsequent event | TNMP
Short-term Debt [Line Items]
Notes payable, related parties			0
Remaining borrowing capacity			0
Consolidated invested cash			0
Subsequent event | PNMR Development
Short-term Debt [Line Items]
Notes payable, related parties			$ 30,200,000