Electric Operating Revenues - Disaggregation of revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 384,493	$ 346,585
Alternative revenue programs	(5,505)	(909)
Other electric operating revenue	65,130	19,031
Revenues	444,118	364,707
PNM
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	275,644	251,206
Alternative revenue programs	(2,065)	976
Other electric operating revenue	65,130	19,031
Revenues	338,709	271,213
TNMP
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	108,849	95,379
Alternative revenue programs	(3,440)	(1,885)
Other electric operating revenue	0	0
Revenues	105,409	93,494
Energy
Disaggregation of Revenue [Line Items]
Revenues	444,118	364,707
Energy | Residential
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	151,942	149,763
Energy | Commercial
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	121,107	111,363
Energy | Industrial
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	31,522	26,193
Energy | Public authority
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	5,952	6,069
Energy | Economy energy service
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	8,940	10,581
Energy | PNM | Residential
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	112,574	114,669
Energy | PNM | Commercial
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	88,004	81,934
Energy | PNM | Industrial
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	23,132	18,900
Energy | PNM | Public authority
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	4,426	4,587
Energy | PNM | Economy energy service
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	8,940	10,581
Energy | TNMP | Residential
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	39,368	35,094
Energy | TNMP | Commercial
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	33,103	29,429
Energy | TNMP | Industrial
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	8,390	7,293
Energy | TNMP | Public authority
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	1,526	1,482
Energy | TNMP | Economy energy service
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0
Transmission
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	60,055	38,624
Transmission | PNM
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	34,526	17,503
Transmission | TNMP
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	25,529	21,121
Miscellaneous
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	4,975	3,992
Miscellaneous | PNM
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	4,042	3,032
Miscellaneous | TNMP
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 933	$ 960