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Construction Program and Jointly-Owned Electric Generating Plants (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) generating_unit	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	$ 616,273	$ 501,213	$ 500,461
Plant in Service	7,918,601	7,548,581
Accumulated depreciation	(2,713,503)	(2,604,177)
Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	341,847	255,627	309,142
Plant in Service	5,753,267	5,623,520
Accumulated depreciation	(2,076,291)	(2,006,266)
Texas-New Mexico Power Company
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	254,006	223,448	$ 145,495
Plant in Service	1,919,256	1,686,119
Accumulated depreciation	(516,795)	$ (487,734)
Joint Projects | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	341,800
Joint Projects | Texas-New Mexico Power Company
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	254,000
Joint Projects | PNMR
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	$ 616,300
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	$ 779,236
Accumulated depreciation	(435,312)
Construction Work in Progress	$ 486
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	$ 819,613
Accumulated depreciation	(369,431)
Construction Work in Progress	$ 31,275
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 | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Number of units (in generating units) | generating_unit	2
Four Corners Units 4 and 5 (Coal) | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 283,939
Accumulated depreciation	(100,137)
Construction Work in Progress	$ 10,794
Composite Interest	13.00%
Luna (Gas) | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 78,258
Accumulated depreciation	(30,255)
Construction Work in Progress	$ 0
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%

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