Financing - Short-term Debt and Liquidity (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) utility	Jul. 29, 2022 USD ($)	Jun. 30, 2022 USD ($)	May 13, 2022 USD ($)	Mar. 11, 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								$ 6,400,000
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			2.77%
PNMR Revolving Credit Facility | WEB LOC Facility
Short-term Debt [Line Items]
Letters of credit outstanding			$ 30,300,000
PNM 2017 New Mexico Credit Facility
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end			2.40%
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
TNMP
Short-term Debt [Line Items]
Letters of credit outstanding			0
Notes payable, related parties			$ 11,300,000					0
TNMP | TNMP Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, interest rate at period end			2.23%
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			3.00%
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	$ 100,000,000	$ 75,000,000
Revolving credit facility | TNMP | First mortgage bonds
Short-term Debt [Line Items]
Collateral amount			$ 75,000,000	$ 100,000,000
Senior Notes | PNM
Short-term Debt [Line Items]
Financing capacity						55,000,000
Senior Notes | PNM | PNM 2021 75 Million Term Loan
Short-term Debt [Line Items]
Financing capacity						75,000,000
Senior Unsecured Noted, Pollution Control Revenue Bonds | PNM | Pollution Control Revenue Bonds, Due June Twenty Twenty Three
Short-term Debt [Line Items]
Unsecured long-term debt, noncurrent						$ 130,000,000
Interest rate contract
Short-term Debt [Line Items]
Number of derivatives | utility	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		$ 6,400,000
Remaining borrowing capacity		644,100,000
Subsequent event | PNMR
Short-term Debt [Line Items]
Remaining borrowing capacity		259,000,000
Consolidated invested cash		900,000
Subsequent event | PNM
Short-term Debt [Line Items]
Notes payable, related parties		0
Remaining borrowing capacity		320,100,000
Consolidated invested cash		0
Subsequent event | PNM | Lines of credit
Short-term Debt [Line Items]
Remaining borrowing capacity		0
Subsequent event | TNMP
Short-term Debt [Line Items]
Notes payable, related parties		0
Remaining borrowing capacity		65,000,000
Consolidated invested cash		0
Subsequent event | PNMR Development
Short-term Debt [Line Items]
Notes payable, related parties		$ 2,400,000