Segment Information - Summarized Financial Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) segment	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information, Profit (Loss) [Abstract]
Electric operating revenues	$ 444,118	$ 364,707
Other operating expenses	131,872	136,271
Depreciation and amortization	75,764	69,874
Operating income	68,068	43,166
Interest income	4,292	3,559
Other income (deductions)	(24,484)	1,930
Interest charges	(26,220)	(25,884)
Earnings before Income Taxes	21,656	22,771
Income taxes (benefit)	2,438	1,566
Net Earnings	19,218	21,205
Valencia non-controlling interest	(3,095)	(3,494)
Subsidiary preferred stock dividends	(132)	(132)
Net Earnings Available for PNM Common Stock	15,991	17,579
Total Assets	8,727,686	7,943,309	$ 8,666,885
Goodwill	$ 278,297	278,297	278,297
PNM
Segment Reporting Information [Line Items]
Number of operating segments | segment	1
Segment Reporting Information, Profit (Loss) [Abstract]
Electric operating revenues	$ 338,709	271,213
Depreciation and amortization	45,790	41,949
Operating income	45,016	33,050
Interest income	3,133	3,595
Interest charges	(14,572)	(12,893)
Earnings before Income Taxes	8,361	24,996
Income taxes (benefit)	823	2,834
Net Earnings	7,538	22,162
Valencia non-controlling interest	(3,095)	(3,494)
Subsidiary preferred stock dividends	(132)	(132)
Net Earnings Available for PNM Common Stock	4,311	18,536
Total Assets	6,040,088		6,060,133
Goodwill	$ 51,632		51,632
TNMP
Segment Reporting Information [Line Items]
Number of operating segments | segment	1
Segment Reporting Information, Profit (Loss) [Abstract]
Electric operating revenues	$ 105,409	93,494
Cost of energy	29,600	26,510
Depreciation and amortization	23,642	22,190
Operating income	24,242	17,025
Interest income	1,182	0
Interest charges	(9,150)	(8,475)
Earnings before Income Taxes	17,211	9,612
Income taxes (benefit)	2,151	877
Net Earnings	15,060	8,735
Total Assets	2,450,081		2,364,772
Goodwill	226,665		$ 226,665
PNM
Segment Reporting Information, Profit (Loss) [Abstract]
Other operating expenses	109,089	107,328
Depreciation and amortization	45,790	41,949
Operating income	45,016	33,050
Interest income	3,133	3,595
Other income (deductions)	(25,216)	1,244
Interest charges	(14,572)	(12,893)
Earnings before Income Taxes	8,361	24,996
Income taxes (benefit)	823	2,834
Net Earnings	7,538	22,162
Valencia non-controlling interest	(3,095)	(3,494)
Subsidiary preferred stock dividends	(132)	(132)
Net Earnings Available for PNM Common Stock	4,311	18,536
Total Assets	6,040,088	5,561,146
Goodwill	51,632	51,632
TNMP
Segment Reporting Information, Profit (Loss) [Abstract]
Other operating expenses	27,925	27,769
Depreciation and amortization	23,642	22,190
Operating income	24,242	17,025
Interest income	1,182	0
Other income (deductions)	937	1,062
Interest charges	(9,150)	(8,475)
Earnings before Income Taxes	17,211	9,612
Income taxes (benefit)	2,151	877
Net Earnings	15,060	8,735
Valencia non-controlling interest	0	0
Subsidiary preferred stock dividends	0	0
Net Earnings Available for PNM Common Stock	15,060	8,735
Total Assets	2,450,081	2,163,250
Goodwill	226,665	226,665
Corporate and Other
Segment Reporting Information, Profit (Loss) [Abstract]
Other operating expenses	(5,142)	1,174
Depreciation and amortization	6,332	5,735
Operating income	(1,190)	(6,909)
Interest income	(23)	(36)
Other income (deductions)	(205)	(376)
Interest charges	(2,498)	(4,516)
Earnings before Income Taxes	(3,916)	(11,837)
Income taxes (benefit)	(536)	(2,145)
Net Earnings	(3,380)	(9,692)
Valencia non-controlling interest	0	0
Subsidiary preferred stock dividends	0	0
Net Earnings Available for PNM Common Stock	(3,380)	(9,692)
Total Assets	237,517	218,913
Goodwill	0	0
Energy
Segment Reporting Information, Profit (Loss) [Abstract]
Electric operating revenues	444,118	364,707
Cost of energy	168,414	115,396
Utility margin	275,704	249,311
Energy | PNM
Segment Reporting Information, Profit (Loss) [Abstract]
Cost of energy	138,814	88,886
Energy | PNM
Segment Reporting Information, Profit (Loss) [Abstract]
Electric operating revenues	338,709	271,213
Cost of energy	138,814	88,886
Utility margin	199,895	182,327
Energy | TNMP
Segment Reporting Information, Profit (Loss) [Abstract]
Electric operating revenues	105,409	93,494
Cost of energy	29,600	26,510
Utility margin	75,809	66,984
Energy | Corporate and Other
Segment Reporting Information, Profit (Loss) [Abstract]
Electric operating revenues	0	0
Cost of energy	0	0
Utility margin	$ 0	$ 0