Stockholders' Equity (Details) - USD ($)		1 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Nov. 26, 2018	Jul. 31, 2018	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Payment of dividends					$ 257,600,000
Line of Credit
Class of Stock [Line Items]
Debt-to-capital ratio (not more than)	70.00%		65.00%	65.00%	70.00%
Public Service Company of New Mexico
Class of Stock [Line Items]
Equity contribution from parent					$ 0	$ 0	$ 0
Payment of dividends					$ 283,500,000
Preferred stock, dividend rate					4.58%
Preferred stock, redemption percent					102.00%
Preferred stock outstanding (in shares)					115,293	115,293
Preferred stock, cumulative shares authorized (in shares)					10,000,000	10,000,000
Public Service Company of New Mexico | Maximum
Class of Stock [Line Items]
Requirement to obtain approval to transfer more than a percentage of PNM's assets					5.00%
Public Service Company of New Mexico | Line of Credit
Class of Stock [Line Items]
Debt-to-capital ratio (not more than)					65.00%
Public Service Company of New Mexico | Affiliated Entity
Class of Stock [Line Items]
Cash dividends paid to parent company by consolidated subsidiaries					$ 0	$ 77,400,000	60,700,000
Texas-New Mexico Power Company
Class of Stock [Line Items]
Equity contribution from parent					$ 80,000,000	30,000,000	50,000,000
Preferred stock, cumulative shares authorized (in shares)					1,000,000
Texas-New Mexico Power Company | Line of Credit
Class of Stock [Line Items]
Debt-to-capital ratio (not more than)					65.00%
Texas-New Mexico Power Company | Affiliated Entity
Class of Stock [Line Items]
Cash dividends paid to parent company by consolidated subsidiaries					$ 55,300,000	$ 41,900,000	$ 44,400,000
PNMR and TNMP
Class of Stock [Line Items]
Preferred stock outstanding (in shares)					0
PNMR and TNMP | Line of Credit
Class of Stock [Line Items]
Debt-to-capital ratio (not more than)		70.00%