Construction Program and Jointly-Owned Electric Generating Plants (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) generating_unit	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	$ 679,028	$ 616,273	$ 501,213
Plant in Service	8,480,799	7,918,601
Accumulated depreciation	(2,835,170)	(2,713,503)
Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	335,055	341,847	255,627
Plant in Service	6,022,753	5,753,267
Accumulated depreciation	(2,158,915)	(2,076,291)
Texas-New Mexico Power Company
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	321,505	254,006	$ 223,448
Plant in Service	2,193,270	1,919,256
Accumulated depreciation	(537,707)	$ (516,795)
Joint Projects | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	335,100
Joint Projects | Texas-New Mexico Power Company
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	321,500
Joint Projects | PNMR
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	$ 679,000
SJGS (Coal) | Unit 4 | Other Unrelated Entities 2
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership percentage	12.80%
SJGS (Coal) | Unit 4 | Other Unrelated Entities 3
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership percentage	8.475%
SJGS (Coal) | Unit 4 | Other Unrelated Entities 4
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership percentage	7.20%
SJGS (Coal) | Unit 4 | Other Unrelated Entities 5
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership percentage	7.028%
SJGS (Coal) | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 780,544
Accumulated depreciation	(448,213)
Construction Work in Progress	$ 659
Composite Interest	66.35%
SJGS (Coal) | Public Service Company of New Mexico | Unit 4
Jointly Owned Utility Plant Interests [Line Items]
Composite Interest	77.297%
Palo Verde Nuclear Generating Station | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 828,191
Accumulated depreciation	(387,436)
Construction Work in Progress	$ 37,235
Composite Interest	10.20%
Number of units (in generating units) | generating_unit	3
Period of time for the original full power operating licenses	40 years
Operating lease, option term extensions	20 years
Four Corners Units 4 and 5 (Coal) | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 301,867
Accumulated depreciation	(100,187)
Construction Work in Progress	$ 7,820
Composite Interest	13.00%
Luna (Gas) | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 76,917
Accumulated depreciation	(29,758)
Construction Work in Progress	$ 57
Composite Interest	33.33%
SJGS Units 1 and 2 | Other Unrelated Entities 1
Jointly Owned Utility Plant Interests [Line Items]
Composite Interest	50.00%
SJGS Units 1 and 2 | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Composite Interest	50.00%
Four Corners | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Number of units (in generating units) | generating_unit	2